Additions/changes to local Mac Music library not saving

Since the beginning of June 2022, all additions and changes made to my local Music library on Mac are not saving in the library file. I can add new songs (purchased from non-iTunes digital retailers) and I can make edits to existing songs, and those new songs/changes will be saved to the actual files/folders in the Media directory, but if I close Music or restart the computer, when I open Music again, none of those additions/changes are visible. This includes new playlists or changes to existing playlists. The "Date Modified" *is* changing on the library file, but the actual changes aren't "sticking." If I've changed something like the title or album of an existing file, the underlying file/folder will update, but since the Library file was not updated, that song will suddenly have the "file not found" exclamation point because the song isn't where Music expected based on the outdated library file.

I have checked the permissions of all files and folders involved.

I do not subscribe to Apple Music or iTunes Match.

Thank you to anyone who might be able to help!

Stuart