The latest version of the Jellyfin Media Player (desktop client) isn't backwards compatible with previous server versions, and it is breaking user's homepages:
https://github.com/jellyfin/jellyfin-media-player/issues/626
Fix is to update the Jellyfin server to the latest version. Please do so. 🙏
P.S. Version 10.9.1 is buggy as hell, so don't update your server. specially without a backup cause you can't revert back without one.