Can’t edit pages or add new

I recently updated to WordPress 5.5.3 and have been having a lot of problems. Initially, I had the white screen of death on the whole page, but I manually redid the install and the page now displays. However, I’m unable to edit any pages, add new ones, or customize my theme. I’ve tried on both firefox and safari and have the same result. I tried disabling all plugins and reverting to the default 2020 theme but no dice. I tried downloading and installing the sitehealth plugin but I’m just getting a spinning wheel. Any suggestions for what to try next?

The page I need help with: [log in to see the link]