Bluetooth setting disappeared from both settings and device manager

For me exchanging the adapter with a spare one lying around helped. I replaced my current adapter booted up and Bluetooth did work again. Aftwards I did a second exchange and my previously not functioning adapter came back to life immediately. If you have the option to do a switch, I would recommend this. Because nothing software-wise did help me to resolve the issue. I had exactly the same issue as the thread starter describes.

Edit: I also noticed, that disabling WLAN via FN keys does completely cut the Bluetooth device (at least on my two Dell notebooks). So it won't be shown in Device Manager and the settings switch is also gone. That might be something worth to consider. The WLAN adapter is still listed but the Bluetooth doesn't show up not even under hidden devices.

I had the same problem with my laptop. I tried most suggestions on this site and others, with no success. What worked for me was unplugging the power to the laptop and restarting. The bluetooth on/off switch reappeared on startup. Bluetooth devices then worked. I could then reconnect power and there was no loss off bluetooth. Hope this helps someone. Cheers, Dave