How I fixed tethering my Nikon D500 and D850 in LR Classic 11.2... in case it helps anyone else...

I hadn't tethered my Nikon cameras to Lightroom for some time - possibly not since 2019.
When I tried to tether my D500 and D850 (separately), Lightroom hung for both cameras at the "Detecting Camera" window - repeatedly - including trying two different cables and three different USB-C to USB adaptors.

I tried the cameras on an older computer running LR Classic 10.3 (on MacOS Mojave) and they both tethered successfully (as they had done in 2019)

Back to the computer with LR Classic 11.2 (which is an Intel MacBook Pro 16" running Catalina 10.15.7)...

I found a post in this forum indicating that I should enable the Nikon Tether Plug-in (using Lightroom File/Plug-in Manager).  But the Plug-in was already enabled.

Here's what worked, and I don't know why:  

1) Disabled the Nikon Tether Plug-in in the Lightroom Plug-in Manager.  Closed Lightroom

2) Reopened Lightroom then Enabled the Nikon Tether Plug-in.  Closed Lightroom

3) Reopened Lightroom and tethering works.

Hopefully this can help someone else struggling with the same problem.

Don