Unfortunately, reconfiguring the provider (removing and re-adding) didn’t work.
I’ve published a Git repository on GitHub that provides a ready-made Navidrome with a song and a cover, including a basic auth Nginx proxy and a Man-In-The-Middle server. To recreate it, just start the stack with docker-compose up, open the Man-In-The-Middle in the browser, connect the app, and play the song.
I’ve included the description and all the passwords used in the readme.