I can confirm it works with the latest changes

It doesn't, the mw_version check in api.Request.add_defaults() (line 1243) still fails.

Change 699152 seems like a cleaner solution, i'll check if it also works for my private wiki / BotPassword case

Ok, i've tried that, but unfortunately there are a few other places in the codebase where calls to mw_version are made:

I've created a pull request: https://gerrit.wikimedia.org/r/c/pywikibot/core/+/699137

After some experimentation, i've come up with a possible fix:

These are the permission settings:

# The following permissions were set based on your choice in the installer
$wgGroupPermissions['*']['createaccount'] = true;
$wgGroupPermissions['*']['autocreateaccount'] = false;
$wgGroupPermissions['*']['edit'] = false;
$wgGroupPermissions['*']['read'] = false;

A self-hosted wiki.