[BG3] If I multiclass Wizard/Sorc, which ability score is used for spell DC, spell attacks, etc?

Given what I’ve read about BG3 allowing anyone with at least one level of Wizard learning any spell for which they have slots, and how 5e in general handles spell slots for multiclass casters, I’m thinking to make a Wizard 1/Sorcerer X character, and using the ability to learn from scrolls to remove the limited spell pool...