Extremely frustrating. Hours of gameplay gone to waste on this. Frustrating enough that I got to the point where I saved between every action and turn in combat. I decided to submit this bug and just stop playing until it's fixed.
When in combat or turn based mode, having a spell/attack selected then going to deselect or cancel that attack using a tap of the B button, the game ends the turn and goes to the next character/enemy in initiative. On Stadia the Hold B is what ends turn.