I was on 12.01. I have done as you suggest but it still hangs on Opening Catalog: Lightroom Catalog-vx.lrcat
Search the LrC forum for "Lightroom Classic Hangs on Opening". There may be previous threads that can help. I have personally never had to deal with that issue.
Be sure the catalog(s) is backed up. Two things you can try is to roll back to V 12.0.1. You can do that in the Adobe Creative Cloud app. Also in the CC app, you can uninstall and reinstall LrC.
I would also reset LrC preferences. Lightroom Classic preferences do not get reset with a re-install. You have to do that separately.