check out the protondb page, maybe something helps
(filter for the appropriate gpu and distro but the latter is less important) https://www.protondb.com/app/212200

idk which mmo it is but i would assume an older engine runs more reliably on linux than a new one

actually, for me, trying and failing to run star wars republic commando a few years ago on win 10 was what pushed me to really look into gaming on linux, and after installing it via steam, enabling steam play, i just clicked play and it ran great, i was shocked
and you can add any windows executable to steam (although it’s a bit janky), enable compatibility, and most of the times, stuff just runs
heroic launcher also is great, but a bit more complicated

why do you need to switch? win+p is the switch between mirrored and joined mode right? why not just let the system handle it?
i too have a few consoles and i use a hdmi switch before monitor 1 and on the 2nd monitor i sometimes switch between hdmi and vga for an older pc, but i just let pop do whatever

what’s “ate”? edit: oh it’s just a type for “are” isn’t it

i would recommend getting an extra ssd, installing a beginner friendly distro (mint or pop for instance) and just boot it up occasionally, see what works, what doesn’t. i got into linux like this, gradually, over years