A plugin for resolving the Wordpress 5.6.1 issue that interferes with updating custom post types (and potentially page, post, etc.)
Install 561.php in your plugins folder in Wordpress.
Because I discovered that we had a bunch of sites that were intentionally running on 5.6.1 and couldn't submit updates to custom taxonomies, so I had to fix the problem in a way that didn't involve touching the functions.php on each site. Thus, a plugin.