Update 2. I narrowed down the problem to my custom users-permissions extensions. When I have src/extensions/users-permissions/strapi-server.js present, I’m seeing the problem demonstrated in my original post. I see that src/extensions/users-permissions/content-types/user/schema.json is updated correctly, but the changes are not reflected in the admin UI.
I can work around the issue by modifying src/extensions/users-permissions/server/content-types/user/index.js instead of using the admin UI which modifies src/extensions/users-permissions/content-types/user/schema.json. When I edit that file, the admin UI behaves as expected. However, I don’t know if it’s good to edit that file. Further, I never had to edit that file in previous versions of users-permissions.
I’m pretty confused on this one, but I’ll keep looking for an answer.