SOLVED (see my post in this thread, or watch this
https://www.youtube.com/watch?v=18SLcnbqwaI )
- - - - - - - - - -
I am stumped. I have a KORG nanoKontrol Studio (mixing board with 8 faders, knobs, sliders) connected to my PC by a midi USB cord. The board lights up so I know it has power. But none of the sliders or knobs have any effect on a track in Reaper.
I have the driver for it installed. The KORG editor software recognizes it and shows all the knobs and sliders for optional reconfiguring/learning. It is set up on midi port 0 as shown in the Korg uninstall utility.
When I look at the Options/Preferences Midi Devices in Reaper (v6.23 Win64), in the MIDI input to make available I see my midi keboards listed with Mode "Enabled+Control" but the KORG nanoKONTROL Studio has its Mode listed as "!!! N/A: Enabled+Control"