This being said, it should be clear that a wizard 1/cleric 19 having access to all cleric and wizard spells can't be the intention.
Well fortunately it doesn't work that way.
1 Cleric / 11 Sorc can only cast level 1 cleric spells.
The game is combining total spell levels for arcane or divine levels, in fact NWN1&2 already did this - 'Your arcane / divine spellcasting raises every level / every other level / every level beyond first'.
Seems to be working as intended. If you think it isn't send a support email.
Also https://dungeonsdragons.fandom.com/wiki/Homebrew#:~:text=See%20the%20list%20of%20D%26D,campaign%20settings%20or%20variant%20rules.
Homebrew is fan terminology for game material made by players of a game, rather than by an official or third-party publisher. In a Dungeons & Dragons context, this often includes new spells, character classes, campaign settings or variant rules.
In DnD, there has never once been any such 'You must follow the official ruleset exactly'.
So technically I could homebrew 40 levels, the same multiclassing as 2e, the same number of spellslots (up to 5 of each level), and metamagics for every spellcasting class if I so desired, as could Larian if they wanted to.
