Possible it's not an OS upgrade issue. When your bluetooth disappears, check Device Manager / USB Controllers to see if an Unknown Device is listed.  If you see one, that's your problem. Here's the fix:

1. Uninstall the USB 3.0 controller. (uninstalling Unknown Device doesn't work. it reinstalls itself.)
2. Full shutdown.
3. Unplug power cord. (left mine for 30 min but prob takes less time)
4. Plug in / boot up.

The system will automatically reinstall the USB 3.0 controller. Bluetooth functionality should be fully restored.

I've been losing bluetooth periodically for months on an XPS 8930. Two days ago, it was the Unkown Device issue (not always the case) and it took me 19 hours, a useless Windows reinstall and a ton of searching to finally get it resolved.

Good luck!

ken have you found the suggested solution work for you? I did a ream of things to solve it which included installing the latest BIOS. The problem has surfaced again just 1 few days after resolving it. Hoping we can figure out what the issue is.

I can confirm Spluck's solution worked for me!!! However I did not plug in upon boot up in step 4. I just used battery power. Bluetooth icons back and my mouse has connected instantly after startup.

I went back to Windows 10 whilst I could. I will try Spluck's solution when i got to Windows 11 in future.

Omg you saved my life, I'm so relieved I could cry! And before this I was on the verge of tears for other reasons. Literally just got a brand new alienware like 2 days ago and my Bluetooth just abandoned me today. I've spent all night trying to fix this, even reset the thing twice, tried reinstalling drivers, did command prompt tests, went into the weird services menu thing to stop/start BT services (I tried basically everything that's out there), but it was your advice that worked! I only left the machine off + unplugged for 5 minutes bc it's 2:30am rn and I was about to give up for the night anyway lol. But it worked!

Thank you sooooo so so much!

Excellente !  Wonderful.  Solved problem on my Acer tower (with Dell keyboard) upgraded to Win11.  Thank you Spluck.

Hello, I see you are looking for technical assistance. If you need our help, you can start a private/direct message with us and we will be happy to assist you.

I was on Win 10 when I wrote that Bluetooth post back in January.  Still running Win 10 and still consistently running into Bluetooth issues.  When the system finally gives up the ghost, I'm going with Linux or Ubuntu. Sick to death of Windows poor performance and insane intrusiveness.

So glad to know that my post was helpful.  I went through all the same stuff as you before I found a fix that worked for me. Can't tell you how many times I've reinstalled Win 10 over this foolishness. Important to know that the fix is not permanent; at least not for me. Don't know the root cause of the issue but every few months my Bluetooth disappears again.

Yall might want to check that the Bluetooth device (and/or the combo Bluetooth/WiFi card) is NOT powering-down due to Power-Management. 

Also, try not letting the computer sleep for a while. See if that helps with the stability of the device.