When I update my library from my WebDAV server (with basic/digest authentication enabled and user:password set) it gives me unsupported protocol error.
Later in the log, you’ll see, I removed user and password and went anonymous, and there was no unsupported protocol error.
Here is the log: https://paste.kodi.tv/bidemibaho.kodi
I’m using wsgidav to host WebDAV server on termux for android.
Can you try on your end and see if this happens on your end too, please?