OK. First 3 domains will be the ones in BG3:

Life, Light, and Trickery

Life - BG3 actually has implemented this one well in terms of there is no difference between Tabletop and cRPG. The Life Domain is the Classic Cleric Domain, where you are the Tank, Healer, Buffer. So, I won't go into too much detail on this because I've already mentioned how BG3 kinda strips this Domain of its effectiveness. Yes, Disciple of Life does add a little extra boost to Healing Spells, and they will become more effective with higher level spell slots, but overall it's still not much more effective than potions that can be thrown across the board at allies. Think about it. The very basic Healing Potion provides 2d4+2 healing. That's 4-10 HP restored with a single potion. Cure Wounds is 1d8+Spellcaster Modifier. So, typically something like 5-12. With Life Domain, that's 7-14. So some buff but not much.

The real homebrew that makes this more effective in BG3 is that you can cast multiple spells in the same turn. So, in D&D 5e, you aren't supposed to be able to cast a Level 1 or higher spell and then cast a Bonus action spell as well. Meaning, in 5e, you are restricted from casting Cure Wounds AND Healing Word in the same round. You can cast a Cantrip as an Action and then a Bonus action like Healing Word, but you can't cast a Level 1 or higher spell as an Action and then Healing Word. So, Larian has offset the Healer Cleric nerf by allowing spellcasters to cast both a Level 1 or higher spell like Cure Wounds AND a Bonus spell like Healing Word in the same round. This does make the Healer Cleric more effective because they can heal 7-14 HP with Cure Wounds and then 7-10 HP using Healing Word. That IS much more effective than a single, basic potion.

Well then. What's the problem? The problem is that by allowing such a rule, now ALL spellcasters can cast Level 1 or higher spells AND Bonus action spells in the same turn. Why is that a problem? Wizard, Level 5 has Level 3 spells. He can now cast Fireball and blast an entire group of enemies doing 8d6 damage, even at point blank with enemies all around him. Then he can Misty Step as a Bonus action to get away and run an additional 30 feet to get even further away. Thus, the wizard is now OP. What once limited the wizard in that he had to choose between either using Misty Step or Fireball, he is now no longer limited in this way. He can do both.

What will this mean for later in the game? Imagine you are facing an enemy wizard at level 5 or higher. You win initiative and run up to him to try to prevent him from casting Fireball on your party. Only your fighter won initiative, so only your fighter gets up close. In RAW 5e, the wizard would likely Disengage and retreat, or use Misty Step and retreat, rather than cast Fireball because there's a good chance that if he doesn't that fighter is going to beat the living tar out of him on the next turn. Action Surge plus 2 Attacks already at Level 5 plus Menacing Attack or some other maneuver. Yeah. Wizard could die in a single round from a fighter moving into close range like that. So the AI would likely have the enemy wizard retreat, like he should, allowing his meat shields to rush in and keep the fighter at bay. This allows other characters, like your cleric, to do things like cast Silence, etc. to try to keep the wizard from hurling powerful spells at you and your party.

So, allowing Bonus + Level 1 or higher Action spells unbalances the entire system, and it's going to be a serious problem for later in the game. What this means is that either Larian has to go back to RAW 5e, and limit spellcasters to Cantrips + Bonus, and thus make clerics not as effective as Healers (barely better than potions), or they'll have to come up with another solution to try to prevent wizards and other spellcasters from becoming too OP. OR... which is entirely possible, they can just not do anything about it, and what you're going to have are super OP wizards teleporting everywhere on the map AND hurling high damage spells - which, to me, will be VERY frustrating. Imagine the Phase Spider Matriarch as a Level 5 or higher mage. Misty Step 30 feet away from enemies. Hurls Fireball. Boom! Party loses half their health. Party tries to Dash to the wizard. He Misty Steps again on round 2 and Fireballs or Lightning Bolts your party. Ugh! Forget Fighters. They'll never be effective against such an enemy, especially if they Misty Step to high ground for +2 AC AND they have Mage Armor enabled AND they use Blur or Mirror Image.

As far as scrolls go, I have heard that Larian does plan to eventually restrict scrolls to proper classes. This WILL make clerics more valuable than current. As it stands, because anyone can cast Revivify and Raise Dead and use any cleric scroll, no cleric is necessary. Between scrolls and potions and magic items, you can do everything a cleric can do as a Rogue, Warlock, Wizard, Fighter, etc. You can even Speak with Dead using the amulet (which is a Bard/Cleric spell only) and cast Bless with the staff you find in the Arcane Tower. I mean, there's pretty much nothing special about the cleric when you start adding all the weapons and items into the game.

So, my recommendation is to restrict the spells like 5e says to so wizards can't use Bonus Actions and Action Spells in the same round, and so Clerics can't cast both Cure Wounds and Healing Word in the same round. Restrict scrolls so only those classes that can cast Revivify and Raise Dead can actually cast them. Stop allowing throwing potions and limit it to using potions ONLY at melee range with your ally - meaning you have to get up close to Use Potion on a friend. This makes it so the Healing Word is MUCH more important and valuable, being able to heal someone 7-10 HP from a distance. Limit how many potions you can acquire as loot, forcing players to purchase more potions if they need them. Thus, adding value to the cleric healer. After all, if you have a cleric healer, you won't have to spend as much money on buying healing potions because THEY are more of a healer to you than potions. Certainly make it so players can purchase a ton of potions, but the point of this is to limit parties without healers so that they aren't AS capable of buying better weapons and armor because they have to focus some of their resources on buying healing potions. If you don't have a healer, you have to pay the price. This vastly increases the value of Shadowheart as a member of the party, or any other healer that you might make.

As for the items and weapons that provide cleric spells to anyone - like the Amulet of Voices which provides Speak with Dead to anyone who wears it, or the Bless Staff of Mystra (can't remember it's name) - I don't think they need to be removed or nerfed. Having an item or two that provides anyone with such abilities is fine as long as it's not overdone. Speak with Dead amulet is a good story item that would be a shame to remove from the game or nerf it so that only clerics or bards could use it. Weapons like these are okay and don't terribly offset the balance and are fun to have in the game, in my opinion. But, again, as long as they aren't overdoing it and providing a weapon or item that pretty much devalues all or most of the cleric's (or any class's) abilities that make them special. The problem I have currently with the items is that a LOT of them are negating the special-ness of the classes. I'm not suggesting they remove the items, but I am suggesting that they maybe tame them down a bit - spread them out so you don't find them so frequently.