Same here, playing on Stadia (4k). I tried it on 3 devices:
- windows 10 PC over Ethernet - no lag
- MBP 16 over WiFi - lag
- pixel slate over WiFi - lag
The lag is not too bad, but still noticeable. I only play on the PC now. I have no idea how to fix WiFi lag.
This. At work, on a Windows PC with a wired connection, the experience is seamless. At home, on macOS over WiFi, it's only playable (without hiccups, I mean) during the night when people are asleep, but it's still not as smooth. I've played through the entire game, as well as RDR2 and the Metro series using Stadia. I have a high-end gaming desktop and would still not want to install these games. Makes the work/play distinction clearer and my machine cleaner.
I've played a little on my TV with the CCU over Wifi but not enough to determine lag, my Mac is hooked to gigabit straight to my router.
They do recommend 5Ghz for Wifi and being as close to the AP as possible. I can image if your AP is behind a wall or in a closet or different floor you get noticable delays as signals come in via reflections rather than directly.
The lag is not too bad, but still noticeable. I only play on the PC now. I have no idea how to fix WiFi lag.