Bluetooth not loaded in system preferences

hdieckmann wrote:

Bluetooth will not load after software system upgrade to Monterey

Have you rebooted more than once since the upgrade...(?)

Do a safe boot if necessary  https://support.apple.com/en-us/HT201262

to test, reboot as normal

I had the same problem (plus Mouse and Trackpad preference panes would just hang, not even create an error like the Bluetooth pane). If all the "quick" solutions don't work (meaning reset PRAM, SMC, restart, ...) then try running the Apple Diagnostic (press D at start-up). If the diagnostic passes, then the bluetooth hardware is working fine, and the only sure-fire solution I've encountered is a fresh re-install of MacOS (back up to Time Machine, start up on another disk or recovery, erase and install, then restore from Time Machine). This takes several hours, of course, but as a last resort it worked for me.