Came here to suggest bundling Gamemode with the Flatpak release, I guess it makes sense to do so in this thread instead of opening another one.
As @Creative Principle has already laid out, gamemode allows for a Game running on Linux to make use of certain optimizations for the time the Game is running.
Integrating it into the Flatpak release should be fairly simple, as there is already a Flatpak package for that.
Best regards