If you want to setup the official GeforceNow app on Linux for gaming, use:
flatpak install -y --system flathub org.freedesktop.Sdk//24.08 org.freedesktop.Platform//24.08
flatpak remote-add --user --if-not-exists GeForceNOW https://international.download.nvidia.com/GFNLinux/flatpak/geforcenow.flatpakrepo
flatpak install -y --user GeForceNOW com.nvidia.geforcenow
flatpak run com.nvidia.geforcenow
Alternatively:
Download https://international.download.nvidia.com/GFNLinux/GeForceNOWSetup.bin