Nevermind ...
I bought another one of my favorite keyboards, just like my Bluetooth one except a wifi 2.4 model that has a small USB receiver. It doesn't need to connect after a reboot (I just tested it, and I'm typing on it now).
If anyone does happen to know how to connect a Bluetooth device from the logon screen, I'd file away that information in case I need it again some day, but don't anyone spend any time researching an answer. 😊
EDIT: Just in case anyone is looking for a better keyboard, the ones I use are from Arteck. They're small on the desktop, being the equivalent of a laptop keyboard on a stainless steel base. They're USB rechargeable, and last a very long time on a charge. About $22 USD at Amazon.
The main reason I use these on my desktops is because I spent most of my time typing on a laptop keyboard. This way, all my keyboards feel about the same.