I updated/flashed the v2 ACCST firmware on my old QX7 internal RF module and now I can bind it to the Archer Plus R8 receiver.Both versions are 2.3.11-otx. I assumed that was the ACCST version 2, but now I'm realizing that is the OpenTX version. I thought I had updated the RF module to version 2, but now I realize I must have not done that.
Looks like I have some homework to do.
Apparently I had wrongly assumed that I had updated the TX internal RF module when I did the X9 Lite some time ago. But until now I was only using a HITEC external module and Hitec (and FRSKY MINIMA) receivers on the QX7. So I never had the need to bind D16 receivers.