This post is mostly about UI, but it is also about overall game mechanics.

I have played NWN 1 and 2. I've played BG1 and 2 and Icewindale. I've played the old Pool of Radiance games and Pools of Darkness. I'm a long time fan of all these D&D RPG games.

I have no real complaints about Solasta's gameplay, UI, keybinds, etc. other than maybe when I use Q and E to rotate the camera it is a bit slow to rotate and it is a bit annoying that every time I zoom in and out I have to re=click on the Party Mode button to lock the camera back on the party leader.

Oh...and I don't particularly like that if I select Ranged attack and I can't actually hit an enemy I can't switch back to melee, or vice versa. So if you accidentally click on your Ranged and switch from Melee to Ranged, you're stuck.

I like this about BG3. I don't have to worry about exploring my options in BG3. I can click on all sorts of things and check out what my chances are of success, switch to something else, check out how that might be, etc. Gives me more flexibility for testing out different moves and learning more what works and what doesn't. So in this regards, BG3 beats out Solasta, and I've given Tactical Adventures my suggestion in the past that they need to give players a bit more room to breathe in this regards. Although I get that a character wouldn't be able to switch weapons and then switch back in a single round, it is frustrating and causes characters to have to skip turns if you are just trying to see if a Ranged Attack might be better than Melee. I also like that BG3 tells me my chances in Percentage. I think that is much more New Player friendly than expecting New Players to know that they have to defeat an enemy's Armor Class to hit.

All this said, taking the UI in BG3 apart piece by piece:

1. Character Portraits don't register when I click on them. Solasta's works every time. Single Click.
2. I have to painstakingly Right Click and select Ungroup on each character portrait to unchain a character from the rest of the party to have them do something different. Solasta is a single click on their portrait and they are ungrouped. To rechain in BG3, I have to Right Click and select Group on each character portrait to reform the party. Solasta is a single click on a Party Mode button.
3. Solasta's got a nice Character Summary window when you select the character right there on the UI. Tells you all the major details you need to know about that character. BG3 requires you to go to the Character Sheet screen to see AC and so forth.
4. Solasta's UI tells you what each separate character can do based on their class, etc. per round when in combat. BG3 just lumps all skills, abilities, etc. into 1 hotbar regardless of your class and what your character can do. So in Solasta, if you are a Fighter with no spellcasting abilities, there is no Cast Spell option on your UI. You have Attack, Shove, Disengage, Use Item, and that's pretty much it. No clutter. No useless buttons. If you are a Paladin and have a Power, a button appears labelled Power, and you click it and pop up a smaller menu of your powers like Turn Undead and Lay on Hands. Boom. Clean. Crisp. All organized for you. No playing around with hot bar and so forth.
5. In Solasta, jumping and climbing is automatic. I select my destination, if my character can go there, they just go there. If an Athletics or Acrobatics roll is required, the game auto-rolls it for me. If my character fails, they fall prone. If they succeed, they continue on as normal. BG3 makes you click on a separate jump button, try to play around with the terrain to make the jump line up to exactly where you need it to, and then click again to lock in where you want to go. Then you jump sometimes ridiculous distances without so much as a roll no matter how far the distance. As long as the game determines that your character has a certain Athletics skill level, you can make the jump without a roll. Only if you drop down does it have you roll and if you fail you fall prone. Otherwise, it doesn't matter if you jump 20 meters or 5 meters. So BG3's jump system takes more clicks and requires more work when all we, the players, care about is that we want to get to a certain destination. So I think BG3's jump system would GREATLY benefit from a jump system similar to Solasta. Just point and click on where you want to go. If your character needs to jump, they jump. If they can't make the jump, the game tells you, like Solasta does, "Your destination is unable to be reached." Plain. Simple. Easy.
6. Disengage works every time in Solasta. If I disengage, no matter how close I get to an enemy or no matter where I move, I am not attacked with AOO. In BG3, because Jumping and Disengage are tied together, not only do my characters unrealistically jump all over the battlefield all the time, but many times my character will move away from an enemy, trigger AOO, and then jump to the destination I chose for them to go to. So even though I trigger Disengage, they still get attacked by AOO because the game determined that they needed to move away from the enemy first before jumping to wherever I wanted them to go.
7. Why do I need a button for my melee weapon, a button for my special melee attack, a button for my ranged weapon, a button for my special ranged attack, and a toggle that switches from melee to ranged and from single to dual in BG3? Half of the time, these buttons don't work properly. I'll click on my primary Melee Attack button and the Ranged icon still appears showing a ghost image of my character looking like they are going to do a ranged attack. So then I have to click on it again and sometimes even a third time. Half of the time, when it comes to dual wielding, the characters default to the Dual setting which causes them to use both actions on an enemy that is almost dead anyway. So he has like 5 HP, I kill him with Sneak Attack, and Astarion wastes his Bonus Action striking at thin air. Solasta's is simpler and easier. I have 1 button for attack. There is a toggle right above the Character Summary to switch between Melee and Ranged. A single radial button next to Melee and a single next to Ranged. I want to hit an enemy. I select Attack. Select enemy. Done. If I have 2 weapons and I want to do a second attack with my Bonus action, after my first attack, I select Attack again. Select enemy. Done. Plain. Simple. No wasted Bonus Actions. If I have a special ability like Menacing Attack Melee and Menacing Attack Ranged, the Power button appears on the UI. I select Power and all special abilities appear labeled accordingly. I click the button for my power, click on the enemy, and done.
8. Action options and Bonus options are clearly grouped together on the UI in Solasta. So you are fully aware what options are what. From left to right your Action options appear first. Then your Bonus options. All clearly labeled as such and even color coded to make it really clear that they are two different categories of options. In BG3, there is no clear designation for what options are Actions and what are Bonuses. You have to hover over them and check to see which they are. It is so easy to confuse which spells only require Bonus actions versus which require Action actions.
9. Then to top it all off, BG3 doesn't even make typical 5e Actions actually Actions. So even if you are a D&D guru you are easily confused as to which is an Action and which isn't because they didn't even keep Disengage as an Action, or Shove as an Action. They made them Bonus Actions and put them all in the same area of the hotbar. It's just very confusing trying to remember whether a Jump/Disengage is an Action or Bonus Action, Shove, Dip Poison, Throw something, etc. Is Throw an Action or Bonus? I can't even remember right now. I think it's an Action. But if it's an Action, why isn't Shove an Action? Aren't they both technically attacks against an enemy? Again, Solasta stays true to D&D 5e rules so if you know 5e rules you will know that Shove is an Action, not a Bonus Action.
10. Solasta makes it so shove can both push enemies away and off ledges but also force them to fall prone and thus be easier for Melee attacks to hit. BG3 only allows you to shove people off ledges and away from you. There is no shoving to make them prone. Well, at least if there is I can't figure out how, so that just goes along with what I'm saying anyway.
11. Solasta's Initiative order actually works, every time. There is no skipping around and bouncing back and forth between characters in initiative order. BG3 glitches, skips characters in initiative order, and if you aren't careful when initiative order is grouped together, you may accidentally skip one of your character's turns because you hit the End Turn button when characters are grouped in initiative order. Besides that, Initiative covers the whole left side of the screen. In Solasta it just runs along the top in order. Clean and simple. Now, I will say, that one thing BG3 does right in initiative is that if two characters are grouped together I can move the second one in order first. So if one is in the way of the other or I want them to go before the other then I can do that. This is nice. In Solasta, several times I've had situations where I wished I could move one of the two before the other. So in that regard, BG3's freedom of grouping initiative is nice. Overall, though, it is glitchy and painful compared to Solasta's which is nice and clean and easy to understand.
12. Sneak/Caution. In Solasta, if you are in Party Mode, you click a single Caution button and everyone sneaks. In BG3, if I want everyone to sneak, I need to select each individual character 1 at a time and select Sneak. Same to UN-sneak.
13. Sneak works better in Solasta. It isn't just some line of sight cones like in BG3. If you start to sneak too closely to an enemy, a little Stealth meter starts to appear above your head. The better your character's Stealth, the slower the meter fills. So a Fighter with 0 Stealth and Disadvantage on their Stealth rolls can't just sneak up and pickpocket a merchant who has their back turned, nor can they sneak up on a goblin or bugbear or whatever and kill them with a single hit. If your stealth isn't great, you get spotted real quick. Also, in BG3, I've noticed that if I'm stealthing it, and I wander even remotely into an enemy's cone, my character has to usually roll Stealth like 3 times before it finally stops. It's very frustrating. I've noticed that any rogue I've created, no matter how good, is spotted while stealthing it simply because the game makes me roll like 2-3 times every time I wander into a line of sight cone. So even if I succeeded in my first 1 or even 2 rolls, I'm usually spotted by the 3rd or sometimes even 4th rolls. Now, I get that it might be Disadvantage that they are accounting for, but this is the only time I've ever seen Disadvantage rolled for more than once. Usually, if I have Advantage or Disadvantage in BG3, it is a single roll and it just tells me if I succeed or fail. (Example: I have Advantage when attacking. In BG3, my Percentage chance of success goes up. A single roll is made. Game tells me if I succeed or fail. Game doesn't show me that I'm rolling twice.) So it doesn't seem to me, at any rate, that it is because of something like Disadvantage.
14. Backpacks have meaning besides just as inventory management items in Solasta. If I pick up a backpack that is better than my original, I can carry more weight in items. Backpacks in BG3 are pointless except to store items like keys and books that you don't want to clutter your inventory. Frankly, I sell them now because they are so pointless to me. I have tabs in BG3 that help me sort items if I want to, so if I keep all my items in my regular items menu and I just want to see my Consumables, for example, I select the Consumables tab. Backpacks, therefore, are meaningless to me in BG3 because they actually make item management more labor intensive since any item in a backpack doesn't sort along with the main inventory. The ONLY good backpacks are to me is to transfer multiple items from one character to another quickly. But then, it takes me just as long to put all the items in the bag as it does just to Send to Astarion, or whoever. So why bother with backpacks? To me, they are just another useless item in BG3.
15. Crafting is simple and easy to understand in Solasta and takes time. In BG3, the few times it lets you craft, it has been very confusing. Pull open the recipe. Try to remember all the items you need to put together. Do it in the right order. Anyone can do it, by the way. It doesn't matter if your character knows how to craft a potion or a sword, every character can craft any item in BG3. Meanwhile, Solasta tells you if you have the right items on the Crafting screen. It tells you on that screen as well whether your character is proficient or not. It tells you what tools you need. All of it is laid out easily for you to see and manage.
16. Time. Exists in Solasta. BG3, time is SO vague that you can take as long as you want to do whatever you want. In Solasta, time is measured and you have exhaustion and fatigue and so forth if you don't rest and eat properly every day. In BG3, whatever. No one cares. Goblins will take a month to attack the grove. It's okay. Just play around with the locals all you want. Crafting takes no real time at all. Make a 2 handed magic sword in some random basement in minutes.

Anyway, there's a lot more I could say, but the point that I'm making in this comment here is to show you what we're trying to say in regards to why Solasta's game mechanics are superior right now to BG3. Overall, Solasta's is cleaner, easier, more functional, more true to D&D 5e, more well balanced, more New Player friendly, more realistic, etc. etc. etc.

So you can say whatever you want to try to defend BG3's current UI and game mechanics, but overall, I hope these points will at least be considered by Larian. Again, I love BG3. I like it more than Solasta. I think overall it has so much more potential than Solasta. I want BG3 to do really well. So I am hoping that Larian will do SOMETHING to improve BG3's UI and game mechanics. It doesn't have to match Solasta. That's not what I'm saying. I just want them to make it more user friendly and more New Player friendly so that the game is cleaner, clearer, more understandable, and functions. If Larian doesn't want Solasta to actually come out on top as the #1 D&D 5e game this year, Larian is going to HAVE to fix the UI and game mechanics. Defend BG3 all you want, but there seems to be enough of us agreeing with this that they need to take it seriously.