In CouchDB 3.0.0, the /_all_dbs endpoint became admin-only. This has the side-effect of Fauxton, the “Browser GUI”, not loading properly for non-admin users, as it starts out by reading /_all_dbs.
The release notes have a section that go into the changes.
This is the code change: https://github.com/apache/couchdb/issues/2576
You can get the previous behaviour by setting the config variable [chttpd] admin_only_all_dbs to false, but that allows even unauthenticated users to get a full list of your databases.
