I've seen this issue being fixed in patch notes, thanks!
The arm is fine with the G9, but you need to buy the Heavy Duty one that is built specifically for G9 due to it's curvature and thus different center of mass. It looks a bit unreal that it can hold that weight and nothing happens to the monitor, but moving it is a bit harder than I thought. Maybe I could play around with some screws to adjust it but I don't really care, since I bought the arm to free desk space, rather than to have maneuverability.
Still some cable management left to do, but I finally have a proper gaming / work station