To Everyone:
This entire affair has been baffling and frustrating and time consuming. By all accounts, I should have plugged in my Openspot2 and it just worked, as it did the first time I set it up about 4 years ago, but it did not. I tried it on Windows 10 and Linux, with no change. I tried it on 2 different routers, with no success. I checked the firewalls, but they were not blocking access. Even so, I disabled them, and still no success. So I suspected it was a problem with ports. As soon as I forwarded the ports (42000-42010), the Openspot2 connected to Brandmeister. Nevertheless, I still could not enter my UID at the sharkrf.link site, and my device did not show up on the Brandmeister website. So, although I was now connecting, the device was still not working properly.
After Tyrbiter's suggestion, I checked UPnP, which was enabled. I figured my router was not as smart as his and this is why his Openspot worked without needing to forward ports. Being a curious soul, I deleted the port forwarding to see what effect this would have. After the router effected the change, I expected to see my Openspot2 go back to the state of endlessly trying to connect. To my surprise, it remained connected. That caught my attention. So, I unplugged my Openspot2 and plugged it back in, expecting to see it go back to the state of endlessly trying to connect. This is when the fun happened.
After boot up, I noticed the slowly flashing green LED, indicating connection, but it was interrupted by a quickly flashing red LED. This lasted perhaps 10 seconds, followed by a short pause of no LED, followed by the slowly flashing green LED. I presume that this was what the device should have done all along without forwarding ports.
Whatever happened during the period of the quickly flashing red LED, I took as a good sign. I connected to my OpenSpot2, clicked on the "SharkRF Link" button, which took me to the sharkrf.link webpage, whereupon I entered my UID and it was accepted. I went to the Brandmeister website and my device appeared there. Everything is now working properly.
I would very much like to know why the Openspot2 would not connect until I forwarded the previously mentioned ports and, once having connected, it continues to work after removing the port-forwarding rule. It is as if the port-forwarding caused the Openspot2 to connect and that once that happened, everything worked as it should have worked all along with no port-forwarding.
I would also like to know what transpired during the period of the quickly flashing red LED. I know it indicates data transfer, so was the device being updated? This is my hypothesis, as afterward, I have a new "Brandmeister Manager" button on the right of the device's webpage, and I have a new "BM Hotspot security settings" button in the "Connectors" tab. Also my default profile name changed from "TestProfile1" back to "default ".
I apologize for this long post but i include these details in case all that I have experienced will save someone else the problems I had. I took me, a n00b, about 3 days to solve my problem. Everyone's advice was good and helpful. Without it, who knows how many head-banging, hair-pulling hours I would have spent.
To ALL, a BIG thanks for all your help.