I recently installed a new card in my old pc (Nvidia 710GT) and I have problems while playing Stadia at 720p resolution or 1080p on Chromium (hw acceleration on).
I have no problems at all streaming a 1080p 60 fps video from youtube, the hw acceleration is working.
Btw, when I play to Stadia, I can start the game normally but, after 20 second or more, the gpu goes crazy and I have a lot of stuttering going on the screen before it goes back to notmal. That is unplayable most of the time.
I am using h264 codec with stadia+ extension.. I am using nvidia 440 proprietary driver on kubuntu 19.10. I tried Nouveau driver.. Nvidia 435.. Right now I can play only with hw acceleration off because of this issue with the gpu.
I haven't this problem while playing other games.