You're on the right path, Dave. There is now an "unknown device" in the device list, and I'm finding chatter at Dell about this. Before I reset BIOS to factory or open the case and remove the coin battery or do a selective system restore (I did that last night and it took a couple of hours, and didn't work) I've found this info at Dell:

Removing the Unknown USB Device and installing the latest version of bluetooth drivers helps resolve the issue.

Shutdown system. Unplug AC power cord and then press power button for 10 second.
Power on system and go to Device Manager.
In Device Manager window, check if bluetooth adapter is detected and installed correctly.
If the Qualcomm QCA61x4A has a yellow exclamation, scroll down, right-click Unknown USB Device (Device Descriptor Request Failed) and select Uninstall.
Browse to the Dell Drivers & downloads page:
Dell XPS 8930
Dell Alienware Aurora R8
Dell Alienware Aurora R9
Dell Alienware Aurora Ryzen Edition R10
Dell Alienware Aurora R11
Select the Operating System.
Under Category, select Network.
Locate the latest Qualcomm QCA61x4A/QCA9377 Wi-Fi and Bluetooth Driver.
Click Download and save the file to your computer.
Open File Explorer and browse to the location where the downloaded file is saved.
Double-click the Qualcomm QCA61x4A/QCA9377 Wi-Fi and Bluetooth Driver setup file and follow the on-screen instructions to complete the installation process.
Shutdown system. Unplug AC power cord and then press power button for 10 second. The power on system.

This is the least painful (versus moving stuff off my desk, moving my desk, opening the now dusty cover, etc.) to try first. The trick to using this method is that while I printed a copy to refer to while the computer is off, I also printed to PDF that I saved on my desktop so I can use the links as they appear in the article to find the exact drivers they point to.

The answer seems to be that somehow Windows knocked out the Bluetooth, this happened after last week's update, but I don't know what it did or how widespread (is this across different computer companies, or just at Dell?)