I do miss the two-player mode of Lemmings on the Amiga. Amiga could support a mouse in every port, so you could both use a mouse while battling each other. One player needing to use a joystick on ‘every other platform’ (which for Lemmings, was every other platform in existence at the time) was vastly inferior.
Basically every other computer either only supported one mouse, or all mice moved the same pointer.
Not saying that this is a generally useful feature, and networking has improved to the point where split-screen games are rare, and in an era where most games have console ports then mouse-control multiplayer games are unusual, but you know. Niche usages.





Some people dual-boot to play games with anti-cheat that doesn’t work on Linux, so a recent “AAA multiplayer” release might skew the numbers for a bit as people boot Windows instead.
Linux installations are slightly higher in the US than in Europe, and much much higher than in China. The “use of Linux online” has a bit of a sinusoidal pattern every day depending on who’s awake. But a big Chinese release - Fallen Feathers, for example - will suppress the Linux percentage for a while as well.
Steam do publish the number of concurrent users as well, it should be possible to multiply through to get roughly the “absolute numbers” you want. I think they publish the numbers of players online for multiplayer games too, and since those are the games that Linux will be locked out of, it might be possible to point fingers at the specific games causing the problems?