Issue
I currently own a Dell XPS 8930 desktop that is using a Qualcomm QCA9377 Bluetooth driver. A number of times now my Microsoft bluetooth mouse stopped working. After ruling out the batteries and the mouse itself I noted that in my device mangager my bluetooth was missing. This is a indicator that something is wrong with the bluetooth. In the device manager I had to enable View->Show Hidden Devices in order to see the Bluetooth devices. I tried a reboot, that didn't work. I uninstalled the bluetooth adapter and re-installed it, that didn't work.
Resolution
I'm still not sure why this works but it fixes the issue everytime. Shutdown your computer and after it's done unplug it for 30 seconds to a minute. After that time, plug it back in and boot up and there's a good chance the mouse will be working. The only thing that I can assume is happening is that somehow something is getting corrupted at the hardware level that gets cleared when there is absolutely no power. This issue doesn't occur frequently but it is frustrating when it does occur (as it just did while I was in a Zoom meeting and couldn't unmute myself :D).