You also should pay attention to the listing we did on the external sound cards that work OK with Audacity.
https://forum.audacityteam.org/t/sound-card-reviews/8375/1
The Mic-In on your computer is expecting a weak, wispy, delicate mono microphone signal and you’re feeding it a massive, powerful, loud stereo signal from your mixer. Not a good match. It’s not unusual for the computer sound controls to lose it and go straight from Way Too Loud to off. Gross overload will do that.
USB External sound cards are your friend.
Koz