Thanks for sticking with me, TheOtherCliff.
I'm still mystified. To be clear, I'm configuring a quad, not a one rotor heli.
I confirmed on a different quad in CleanFlight that my transmitter's right-horizontal stick movement works in that it distinctly responds in the CleanFlight Receiver configuration. This was to rule out transmitter hardware failure.
Yet, in LibrePilot, still no go. I tried a second cable from the ReceiverPort, with the same PWM pin arrangements, no change. In PWM, that right-horizontal stick movement translates to Channel 3.
I tried PPM_NoOneShot with the same cable, from ReceiverPort with first three pins connected to the PPM pins on my receiver. All channels respond, but no response on Channel 3.
Then, I tried something different by selecting PPM_PIN8+OneShot. I moved pin 8 to the signal of pin 1, and inserted the plug onto my receiver's PPM pins. Still no go for Roll, on Channel 3.
So, as far as I can tell, I've tried PWM and PPM. Of note to me is that with PWM, the channel arrangements seem to be xETR (with "x" being the missing Aileron), but with PPM, the channel arrangements seem to be ETxR.
Any other ideas?
Attached is a screenshot of how far I got with the PPM config.