@Blackheifer, you're correct according to 5e RAW, but not necessarily according to BG3 rules.
I wouldn't be surprised if @Merlex's suggestion will be possible. Currently in BG3, I believe you can use both bonus actions to attack (?) and cast both a bonus-action and standard-action spell in the same turn (?). Idk if this has been changed since I last played or I'm remembering incorrectly...
Alternatively, it's likely that Quicken might be implemented similar to Sneak Attack, with a dedicated icon that is usable only once per turn.
