Network drives aren't visible to Jellyfin

A library on a mapped drive such as Y: comes up empty, or Add a folder says "Jellyfin can't see Y: while it runs as a Windows service".

Jellyfin's Windows service runs under a built-in account that can't see your mapped drives or your saved network passwords. In the Check-up, tick Network drives, then review and apply. Jellyfin then runs as you, while you're signed in. After a restart, it starts when you sign in.