Ok, I solved the issue, but it's weird how it all worked out. I appreciate ALL the help I've received here and the Dell rep Rahul! I tried just about everything, including system file checker and checkdisk, and resetting the RTC clock, and discharging flea power (which I had never heard about before, but I guess is similar to removing the button cell battery on older motherboards). Nothing worked. Bluetooth wouldn't even show up in Device Manager, even though bluetooth checked out as fine in the BIOS scan. So what fixed it? I don't know -- but it seems to be an issue with a USB hub that had been plugged into my USB-C port. When I record online content, I set up in my studio and connect to all my equipment on a hub. I think I had removed the hub while the laptop was asleep last Tuesday (17 Feb) and all the problems were after that (while not connected to the hub). After days of trying to get it working, today (20 Feb), I went back into my studio and as soon as I plugged my USB hub back into my USB-C port, my bluetooth suddenly came back. I've since unplugged from the USB hub in my studio and my bluetooth continues to show up in Device Manager and work just fine. So, in summary: Just glad to be done. Time to go back to Borderlands 3! 
Yesterday, I was using my paired bluetooth headphones (Bose QC35), no problems. Today, nothing. I had basically come to accept my somewhat buggy system, hoping that it was more a Windows 11 problem than an Alienware problem. Never trust a new Windows until the first service pack, right? But this is getting really frustrating. I guess I can live with these various issues and just shut down my system as a makeshift "hibernate" mode. But I really want my bluetooth back. Any idea what's going on with my bluetooth or what I can do next?
m15 R5, no Bluetooth and other issues