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
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