I've used Stadia in both my main PC and the Chromecast without isssues at all, then i tries to run It on a second, cheaper PC wich i use a media center connected to my TV, It has a ryzen 1200 processor and an RX 560.
Sadly, the 560 doesn't support VP9 decoding and so i'm stuck at 1080p.
Using the unofficial Stadia+ extension i'm able to reach 4k resolution, but in that case the decoding Is handled by the cpu, wich isn't powerful enough (and of course, it's unplayable)
So... Why can't 4k be enabled for h264 codec too? I would use more data, but at least the gpu should be able to handle it