IBD cat stopped pooping in the box, need tips to help.

I’ve been to the vet and my cat was diagnosed with IBD last November. She has never pooped or peed outside the box. Only in the past month has she started pooping outside the box; she still pees in the box. There haven’t been any life changes in our house (we haven’t moved, no young kids, no new pet, no new noisy appliances). I have tried a number of things… Different litter, extra boxes, safe open locations of the boxes, even a litter box buffet, with 3 litter boxes with different litters for her to choose from. Despite all of this, she is still pooping outside the box. Not right beside it, but in different areas of the house. And she doesn’t do it in front of us. Recently, I have also tried confining her in the bathroom overnight with her bed, food, and water, and 2 litter boxes to choose from, but she ends up holding her poop overnight and then poops in the house the next day.
Does anyone have other tips I haven’t tried? Please and thank you.