Before you try other troubleshooting steps, make sure your internet has a connection speed of 10 megabits per second (Mbps) or greater. Even if you’ve signed up for an internet plan of 10 Mbps or greater, we recommend testing your connection on the device you’ll use in the location where you want to play.
Learn about your connection status.
Learn about data usage, bandwidth controls and ISPs.
Your Google Chromecast Ultra, computer, or phone might have a weak internet connection. To improve the connection, here are some things you can try.
Tips for improving game streaming quality
Tip for improving screen distortion
If your screen seems stretched or out of bounds, or Stadia notifications appear cut off, set your picture size to “screen fit” and disable overscan in your TV’s settings. On certain TVs, the "16:9" picture size implies overscan. Check with your TV’s manufacturer for instructions.
If your Stadia Controller is slow or unresponsive, it might be having trouble connecting to Stadia. To resolve issues like missing or delayed button presses, here are some things you can try.
1080p is the max resolution currently supported on PC/Chrome, so that's normal.
Maybe try different USB ports and/or a different mouse. Also check your OS mouse settings.
I play on PC/Chrome78.0.3904.108 with wired kb+m without issues.
EDIT : Disabling hardware acceleration in chrome flags did the tricks. Still no idea why.
This definitely needs addressed:
All bad reviews from Stadia are due to the poor bitrate management presets you are using.