Strange bug with the Stadia app on the Pixel 4 XL, and only connected with my provider (SFR France) router on 5Ghz wifi :
impossible to start a game, each time, I have the message to check my connectivity.
I use the same network to play over the chromecast or my chromebook without any problem.
I think there is a problem with this particular router, as the game starts when I use my wife's phone as router.
Anyone in France with SFR ?
check the tcp/udp port requirements for Stadia and expose those ports and test again. About all that comes to mind, not sure what characteristics there are for a SFR router as I no longer live in Paris.