I’m going to be without my road bike for about a week and was curious if anyone has ever tried to run a bike with GX derailleur with an 11 speed cassette on a direct drive trainer? I’m not going to go buy a 12 speed cassette to ride on my trainer for a week…
If it doesn’t work, I guess I’ll just have to do very short rides outside next week 
I run a 12 speed red xlpr and a 12 speed Dura ace derailleur on my wahoo trainer with an 11 cassette. I use erg mode because shifting is not the best. I should probably buy a 12 speed cassette
I plan to run erg as well. I’ll give it a go and see what happens. I appreciate the response!
I was thinking I hadn’t done this but remembered I had. wheel on but I put my 12spd bike on my dads trainer with his 11spd trainer wheel. Just figured out which gear made the least noise and did ERG. not sure if you needed additional confirmation but now you have 2 examples.
The more the better 
Thank you!