It’s basically like the game-mode optimizations on win10 and Android, temporarily makes the OS more like a console firmware.
As explained here gamemode/lib at master · FeralInteractive/gamemode · GitHub
It can be done with gamemode_client.h or libgamemodeauto.so to make the games run faster
Feral gamemode is included by default on Ubuntu and it’s derivatives (like elementary OS and Pop_OS),
It’s a means to get a performance boost that, in my noob opinion, should be easy to use, and think that GDevelop should use it at least on the “native” games, or maybe let the dev choose if they want their game to run faster or not.