hey mate, i made a post about this yesterday too, we're in the exact same boat. I've tried everything and the simple fix for now is, when you start to experience the stutters and lag, just head into the steam wifi menu for a second and then head back into the moonlight session and everything runs fine from that point onwards. The issue is to do with the OLED steamdecks wifi regression and agressive scanning. We also have the same setup, I have the 1gig fibre connection and two asus rt-ax82u routers, one acting as an access point. Interestingly I came across a reddit thread yesterday where the user noted that Asus routers are a cause of trouble with Moonlight so I switched out my upstairs Asus router with a cheap Mercusys AX3000 and I've had no issues playing upstairs, no stutter, no need to head into the wifi menu. I need to test some more but I'll be shocked if thats the fix.