Music app in Catalina - cannot change song details

Thank you again for helping. I closed music and reset permissions again. I don't see any tmp files and have no third party software that I know of. A screenshot from when I open the package is :

Thanks again. Ah you may have solved part of this - I missed your note about AirPlay in you post about permissions etc - I switched to computer speakers and have been able to update details. As this is intermittent it is too soon to declare victory though.

My library is still missing as in screenshot below. I have also signed out of my account to see if that changes anything but no difference.

Thank you tt2 - I tried the repair permissions to both my music folder (and enclosing files) and also the external drive that stores my media but still have the same issue. would it matter whether I had music open at the same time? i.e. should I be quitting music, make the changes, restart the Mac? Any other suggestions? Many thanks Mike

Thank you again for helping. The only hidden file seems to be the sentinel file at the top and the Shift+Cmd+. toggles that file to visible/hidden. The same issue happens when I import new music so I don't think it is the MP3 tags. Is there a way to validate/rebuild the library without losing my history. Should I try creating a new library and see if that works OK? This has been gradually getting worse over the past 16 months or so since I switched from iTunes to Music.

Thank you I think there were 2 separate issues - 1) the not changing the tags and 2) the initial load of music. For the tags (1), it looks like your suggestion about AirPlay is the solution - I usually use AirPlay and now that I just use computer speakers I have been able to make changes for last couple of days. For the initial load screen (2), I do not use Apple Music but if I leave Music running overnight it does load everything; when starting Music all my music playlists are OK. What I discovered this weekend is if I right click on any of the items under library (eg Albums or Songs) and then select "update smart playlist" it is all fine after 1 or 2 seconds - so it looks like the Albums/songs/recently added etc under library are non updating smart playlists. So I just need to do the right click every time I start Music and it iOS OK. Not sure what I did to get that to start happening! Thanks again for all your help

I agree. Curious as to why they suddenly stopped auto update about 6 weeks ago - I assumed a short glitch after one of Big Sur updates but it has not gone away. Not a big deal though as can workaround with the right click and also created a smart playlist with all my music as well. Thanks again for your solving my bigger issue. Mike

I will try the safe restart at the weekend - any specific validation checks that you recommend as all I have used is Disk Utility to check the disc in safe mode. Thanks again