I have a friend who is using the GR9 with a Shimano HG-601 chain and Deore M5100 11-51 cassette and everything is fine with this configuration, it was a matter of making fine adjustments. Follow the video in PT-BR:
In my case, I use the GR9 with two 46/30 chainrings and an 11-34 cassette and on heavy gravel sometimes the chain jumps a little hitting the frame, what I did was adjust the cage to be more taut, tightening the screw of image:
Thanks for the tip, maybe it's a skill issue on my end. Or possibly made worse by a slightly draggy freehub.
In any case I got an ok deal on a grx812 and that's completely fixed the issue.
Maybe I'll try with the gr9 again in the future when I have time to play have a closer look at it.
Edit:
Actually looking at photos of the gr9 a bit more closely, I'm wondering if there's an two versions?
I've got the first one with no cylindrical part. The second one has it, which looks a lot like some form of clutch/damping.