You can now use Geforce Now on your Linux machine with this quick little trick.
Here the Link to install the User Agent Switcher for ANY Chromium based browser. I used this on Brave and it worked perfectly.
Install this Extension and launch options!
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 Safari/537.36