Music Library Disappeared

I recently updated to Big Sur on my iMac, I had plugged in my iPhone to sync a new playlist and everything seemingly did what it was supposed to do, then I noticed playlists were missing, I quit music thinking that if I relaunched the program it would find the playlists and all the music on my iMac had disappeared. I contacted apple and they weren't really much help as the music wasn't downloaded from Apple Music nor was it purchased through iTunes (except a few songs, even those don't show up), it's all from CDs or Backed up music on Hard Drives which I can still access.

I have made sure the check box for sync with cloud music has been checked but every time I shut down my system or put it to sleep the music disappears again and I have to try and start again which honestly is really starting to **** me off, does anyone have a fix for this, I don't mind if I have to re-add the music again I just don't want to add it all again and lose it all and keep continuing that cycle.

Thanks