I love Stadia but had lot of stuttering and huge drop in frame rate but I found the solution (at least for mac)
Since I did this, I have not experienced any stuttering at all and now enjoy FPS to the fullest (mouse and keyboard)
- Disable location Service
On mac, click on the mac icon then :
-> System preferences -> Security and privacy -> Privacy -> uncheck "Enable location service".
Since I did this, I have experienced absolutely no stuttering at all
I see! Well one thing that helped me get smooth gameplay over WiFi was to use a WiFi analyzer app to find a clear channel and then go into the router settings to switch to that channel. It's especially important if you live in a congested area with lots of neighbors. I do this whenever I plan to play for a while on WiFi.
Also blocking the mic permission in chrome for Stadia.com helps, but that might be just a Chromebook issue.
Also, making sure you are running with no extensions, nothing open except Stadia, and NOTHING running in the background.
Hope something here helps.