That’s a sweet system, Mark.
Have you tried the OBS workaround stated in Dave_ ZPCMR’s post?
Perhaps Dave (the other Dave) could start a fresh thread, and we could post our computer settings, in order to help Zwift look into it.
Your system sounds nearly the same as mine (except I have the RTX3060).
And the word “flicker” is not a perfect description, although it is one word.
To me, it’s a timing issue with hidden surface removal, the Z-dimension of computer graphics. The avatar becomes semi-opaque, and some of the background can be seen thru the avatar.
Try the OBS workaround if you can. and Good luck.