Hey there IVIako,
Thanks for reaching out to Apple Support Communities. I understand you’re no longer able to search Apple Music in Music on your Mac. I’ll be happy to help.
From the Mac menu bar, click on Music > Preferences and then Restrictions. Make sure Apple Music is not disabled there. Under the General tab, see if Sync Library or iCloud Music Library is enabled. Then check Music > Account and make sure you’re signed in with the correct account there.These links have more info:
Change General preferences in Music on Mac
Change Restrictions preferences in Music on Mac
If the issue continues, make sure macOS is up to date:
How to update the software on your Mac
If you’re still not able to search Apple Music, see if this option appears in safe mode and a new user account:
Use safe mode to isolate issues with your Mac
How to test an issue in another user account on your Mac
I hope this helps.