This is a seemingly common problem and I viewed the dozen suggested posts before posting this but none of that helped since it was mainly things I already tried.
50 GB worth of MP3s in /sdcard/Music I can see all those files in various file browsing apps and terminal emulators but no music player app can see them. I tried three different players already. They can see music files in Download directory but not in Music. There was a .nomedia file in there but I deleted it days ago and re-scanned media multiple times and rebooted multiple times. I had all this music in the same location on my last phone Pixel 3 Android 9 but then got a new phone Pixel 5 Android 11, moved all the files onto it, just via file copy from Windows, but player apps can't see them. It's almost as if that .nomedia file was still in there, totally invisible to me.
.nomedia
files are not always visible. Try this app to scan and remove those //Next step, from your settings, show system apps and then locate media storage delete it's data (you won't lose anything), reboot, wait for a while and check //Other possible causes - windows file copy (does not Pixel 5 copy these files over using the transfer function with the cable provided)?;// – beeshyams Dec 07 '20 at 04:09