I've watched several videos on BG3 multiclassing. They all said that if we multiclass, we won't necessarily gain all standard abilities of our second class, but did not mention any specifics.

So I have this idea for a sorcerer who takes 3 levels of Rogue, subclasses into Thief to gain the additional bonus action, so that once they've acquired the necessary sorcery points, they can use their metamagic to cast up to three leveled spells per round once in a while. Having the Rogue's higher number of skills would also be highly appreciated, and since I tend to swap CON for DEX as secondary attribute when I play sorcerers anyway I'd not have to sacrifice a lot in attribute points either.

The question is: if I multiclass into Rogue, will I be able to subclass to Thief and actually gain that extra bonus action? Or is this one of those abilities I won't get?

I haven't the slightest idea if this would be feasible in practice if it works, but if isn't even possible I can stop thinking about it. Does anyone know?