If you want a stroganoff, go for a mushroom version then, which means get rid of the olives and tomatoes. Add a little Dijon for acid and flavor.
You keep saying vegetarian, but the context implies vegan. What is your goal? If only vegetarian, then add some cream or butter. Adding cheese changes it from traditional stroganoff to generic American casserole, which can be delicious.
Right now I’d say your recipe is half way between a mushroom casserole and a chili. Those don’t sound like good combination. Pick one and commit in that direction. Also, using canned and frozen veggies in an instant pot is going to result in some very mushy food without their distinct flavors. You might want to opt for the fresh versions of some things, namely onions and mushrooms.