iTunes Music Library Disappeared - only showing older version?

Just spoke to Apple first line support, they can't escalate my case unless I upgrade to Big Sur, which I want to avoid at the moment. I can still see all the new songs I've added in the Music/Itunes/Itunes Media/Music - so I could easily just add them manually back to my playlist. It doesn't recover all the playlist work I had done, nor does it identify the problem so I can avoid it in the future. I might just take regular backups of the Music Library.musiclibrary file to be safe. Unless you have any other ideas? Thank you

Thanks for the prompt reply. I have read through that page but nothing worked. All my files seem to be last modified in August, which is as strange as it sounds. There are no other backups/versions. And as I stated, this issue is also present on my Time Machine from 9 November. I'm thinking my music library file may be stored in a custom location (but nothing comes up in the search and I'm certain it was standard because I setup my library only a few months ago), or there has been some bizarre corruption/restoring of my music files to an older version. I'm hoping someone has come across this before...

"Did you use the shift-start-Music method to access the old .itl file again, or just open Music normally?"

When I first opened Music today, I just opened it normally. Then, when I realised my library was missing, I closed it and used shift-start-Music method to locate the Music library file. However, that file was also an older version.

"Do you know where the active Music Library.musiclibrary file is supposed to be? Is that location covered by Time Machine?"

When I use Music now, it is updating the file in Music/Music - but still an old version. When I look at this file on Time Machine (9 Nov), it is showing last modified 11 August 2020 which doesn't make much sense.