I'll admit I'm stumped. MacBook Air claims to have lost Bluetooth. There's a squiggly line thru the icon on the menubar & when selected a message reads "Bluetooth not available." Yet if I boot from another SSD of an earlier OS version, it's fine. Tried Time Machine backups, repairs to the directory via DiskWarrior, resetting the SMC, removal of the Bluetooth .plist file followed some 10 minutes later with a restart. Nothing works.
I had this problem previously with the now dead MacBook Pro but I can't recall how I fixed it.
I have a Genius Bar appointment for Friday afternoon at the nearest Apple Store.