You can now use Geforce on your Linux machine.
Install User Agent Switcher Extension

Add Chrome OS User Agent
Add the User Agent String:
Mozilla/5.0 (X11; CrOS x86_64 13099.85.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/84.0.4147.110

Switch Agent and Launch
- Click on the Extension icon and select COS or whatever flag you made.
- Then Launch https://play.geforcenow.com/