You know, the UI wouldn't need that much tweaking really. Party pics bottom left, then navigation action buttons like jump, group chain/unchain button, stealth button (if group chained, all stealth together, and if unchained only those chained stealth), a turn-based/pause button, then three menu buttons.

The first menu button is for weapon actions/bonus actions. This hotbar menu could be accessed via a single hotkey (default is Left Shift key). 12 slots in total auto-arranged for you but completely customizable if you want to. So, standard melee and ranged attacks, plus any special melee ranged attack actions would be listed here including Sneak Attack, Off Hand Attack, Menacing Attack, etc. And here's an idea, why a separate button for Melee Menacing Attack versus Ranged? Why not a single Menacing Attack button, and if you have your melee weapon out, it works with that, and if you have your ranged out, it works with that. Same with Sneak Attack. This cuts down on the number of buttons needed on the hotbar. Finally, an option to expand the hotbar beyond 12 without hotkeys. So, first twelve slots are all hotkeys so a player could hit the Shift key to pull open the menu and then use 1-0 and - and = to activate any of the 12 slots for quick menu popup and slot activation. However, if you really need more than 12 slots, for later levels, you have the ability to expand.

The second menu button is for special abilities like spells, lay on of hands, turn undead, sorcerer points, etc. Same as with weapon menu except hotkey by default is Left Control key. Totally customizable, but auto-arranged with Cantrips first, then prepared Level 1 spells, prepared Level 2 spells, etc. 12 slots with the ability to expand here as well. So, quick access the menu by hitting Left Control and then numbers 1-0, - and = keys. Reactions could also be managed here.

The third menu would be for items with same functionality except hotkey by default is Left Alt Key. Items are auto-arranged based on most commonly used like healing potions, potions of speed, etc., to scrolls and so forth again with the ability to customize it however you want.

Three easy buttons to pull open three separate menus for better organization would make it more user friendly and less of a cluttered, confusing mess. Hotkeys assigned to the three menus would cut down on the need to point and click on everything. A better auto-arrange system would make it so players don't standardly have to spend tons of time organizing things.

And shoot! You could even have a 100% user customized hotbar, similar to what they've given us now, that isn't auto-arranged at all based on using the number keys without shift or control or alt, and the player could put whatever they want, their most used actions, etc. on that single, 12 slot hotbar for a total of 48 hotbar slots; 12 for weapons, 12 for spells and abilities, 12 for items, and 12 for whatever you feel like.

So, like I said, it wouldn't have to be tweaked much. They'd just need to maybe do a few things to organize actions better so I don't play as a rogue with scrolls being dumped into my hotbar randomly because I had my rogue pick them up and then my off hand strike and Sneak Attack are on a whole separate hotbar list so I need to click on the down arrow to access them and so forth.