Here's a good read that summarizes some of the theories about
what causes UC. If you've read hw for years, then most of these have been discussed. It is a bit difficult reading at times, it's within a scientific journal, but some might be interested.
Uncovering the cause of ulcerative colitis
Aug 2019
https://www.ncbi.nlm.nih.gov/pmc/articles/pmc6684508/