Recent testing revealed that Arch Linux, Pop!_OS, and even Nobara Linux, which is maintained by a single developer, all outstripped Windows for the performance crown on Windows-native games. The testing was run at the high-end of quality settings, and Valve's Proton was used to run Windows games on Linux.
Anticheat isn’t malware. Malware has adverse effects on your system.
AC uses some techniques that some forms of malware also use (but far from all)
Malware defined as any software that does not benefit the user but wastes systems resources would fit here.
Anticheat benefits the users by…reducing the number of cheaters in games. Big concept to wrap your head around, I know.
There are several forms of anticheat. The ones that just run when the game is running, is usually fine. However, there is the Riot anti cheat which just runs all the time and isn’t uninstalled when Valorant is uninstalled. That is malware.