Can't Point Music Library at NAS Drive

And that still works.

i am running regular backups of the library file now that I can go back to if needed (and I need to way to often).

however, having a very similar setup my music library does not sync with iCloud music anymore without screwing everything up.

i agree that the experience is getting worse with each new version of iTunes/music / macOS.

i am back to syncing with a cable and through the (now) finder music sync to my iPhone.

Having a library on an external drive is good but can have this problem, particularly if it is a NAS. If the external drive or NAS is not fully mounted, or is asleep, when you start Music, it will default to looking on the boot drive. Some people have resolved this by using a double alias. Make an alias to Music and put this on the NAS. Make an alias of that alias and put it in your Dock. If you start Music using the Dock icon and the NAS is not mounted it will pop up an error message instead of changing your settings. I suppose an even more elegant method would be to use an Applescript to make sure the NAS is mounted, and if it wasn't, to mount it and then start Music.

In the old days you would hold down the option key while starting iTunes and select the library file (.itl) whever it was located.