Hotbar management is very important for me, so I decided to compile some suggestions and bug fixes. feel free to replay with more suggestions and bugs.
Have an option in the settings where you can increase/decrease the number of rows.
Add in the settings alternative ways to cast higher-level spells: I got 2 ways in mind for now that would be great imo: The first option would be to have a button that if you hold it when pressing on a spell in the hotbar it would open a dropdown menu where you chose a level to cast the spell. Another option could be that when you left-click the spell logo again it would increase the spell level and right-click to decrease the spell level (the max level spells in the full game would be level 5 so the max amount of clicks would be 4). The second option might not sound the best but they are currently working on keeping fights as fluid and fast as possible so having you double/triple click a spell to cast it at higher levels is a good way to do it.
Add an option in the settings for it to auto-sort your hotbar per spell level (the first row would be cantrips and class abilities, the second row would be first level spells, etc...).
This one is very minor but I got used to it from dos 2. Basically in dos 2 when you open the spell list the hotbar is temporarily unlocked and I would love to see it in bg3.
The + and - buttons completely mess up all the rows (except the first one). The way it should be handled is either move the spells to the left when decreasing and if there is not enough space then just de slot the spells that don't have space or just de slot the spells that are on the rightmost column.
Reloading saves unlocks the hotbars of all characters.