It's natural the official early access forums are seen as more "toxic". People tend to focus on the things they don't like and want changed significantly more in a place they are (more) likely to be heard, than praise what most agree Larian does well.
I see 3 large issues:
Combat. Excessive environmental shenanigans and excessive bonuses for higher ground/flanking advantage. In particular jumping to flank and gain attack advantage, and putting weapons on flame. Both are virtually guaranteed extra damage, but require the player to perform the same time wasting, boring ritual over and over and over again. This is bad gameplay and is likely to cause class imbalances too (ie barbarians reckless attack ability is rendered worse than useless). Excessive environmental effects may be fun, but also takes a dump on class balance (everyone can fireball) and takes the focus away from the class development. Just think that Larian hasn't found the right balance between what worked well in DOS2, but works less well in BG3.
Resting mechanic. Wrecks immersion and class balance. Either implement it properly with camp changing after location and preferably a day/night cycle like the original games,and/or implement some magical camp like the "Rope Trick" spell that creates an extradimensional space, and/or make evermore house rules to buff the classes relatively nerfed. Alternatively, scrap the mechanic and implement cooldowns and action points like DOS2. The current balance is neither here nor there. Address narrative dissonance between allegedly being in a desperate battle against time and unlimited sleep.
Loot focus and inventory mini-games. Weakest part of DOS2 makes a comeback in BG3 sadly. I would prefer an abstracted system with a party inventory which automatically sorts and stacks by loot type (not accessible in combat). Secondary personal inventory (accessible in combat) should be limited to a smallish amount of hotbar quick slots. Less trash loot. Items that can be used for crafting should be clearly marked as such (in DOS2 you were worried selling items would ruin crafting). Heal items should be scrapped or abstracted to be used automatically after combat (ie. give slow regeneration). Healing related to class abilities should be buffed to compensate classes that are made less useful by the easy access to sleep/heal.