How old is your notebook? When I first played Stadia on my 6 year old laptop via wifi, it was laggy as heck for me. Recently I bought a USB wifi adapter and the performance have improved drastically, comparable to playing on the CCU wired.
Make sure to turn on hardware acceleration in chrome. If using nvidia gpu go to nvidia control panel manage 3d settings and find chrome.exe under program settings tab and set low latency mode to Ultra. Then go to power management mode and select Max Performance. Hit the apply button and Bam the thing should run like you have a chromecast ultra plugged into monitor if not better. 🤓