I want to make ratatouille in my InstaPot

I'd consider using the slow cooker aspect of the instaPot, but not the pressure cooker. I am not a pressure cooker person, but beyond that, I'd be worried about the vegetables turning into mush. Slow cooking will allow you to ignore the vegetables for a while.

Dear sweet Pierino, let me explain my motivations.
1) I was given the Instapot as a gift, so feel compelled to use it when I can.
2) I have a limited amount of energy today--my authenticity is focused on baking 5 loaves of sourdough, a coffe cake for a bereaved friend, and granola--so I am not going to cook each veg separately anyway. The next time I will have a chance to cook like this is next Sunday, by which time the produce will be compost (work keeps on getting in the way of life).
3) I really don't want to wash all those pots and pans--the Provençal are probably rioting at the thought, but I've never cooked the veg separately. Six batches of dishes already and it's only 3 pm.

Maybe I will roast the veg? The oven will be hot anyway.

For traditional ratatouille the vegetables are cooked separately. I'm trying to be open minded here but I can't quite see the benefit of then dumping them in a pressure cooker.