Stop caring about native. It seriously just doesn't matter anymore.

XIV Launcher is the easiest way to get FF XIV running, plus it can link to your phone to almost automatically handle OTP (no typing it in, your phone just sends the code over your local network), but you could also just install the trial inside Steam, should work fine.

Copypasta time. "Did you know that the critically acclaimed MMORPG Final Fantasy XIV has a free trial, and includes the entirety of A Realm Reborn AND the award-winning Heavensward and Stormblood expansions up to level 70 with no restrictions on playtime? Sign up, and enjoy Eorzea today!"

Again not natively unfortunately, but Guild Wars 2 runs pretty well, even on the steam deck!

The base game is free to play, so no problem in testing it.

I don't know about natively, but I've played both FFXIV and EVE Online in Linux in the past, and they ran well, but it's been a little bit.

Project gorgon as others have said is the first native game that comes to mind. Guild wars 2 runs great on proton and that's my recommendation. FF14 is great if you don't mind the subscription and can get through the vanilla campaign, which is a massive slog and a major setback in the quality of the game IMO. Guild wars 2 is a similar situation in that it's a slog for the personal story, but after that it picks up and that's only like 40% of the vanilla campaign as opposed to the whole vanilla campaign of FF14. The FF14 fanboys don't want to talk about the vanilla campaign and for good reason, it sucks, it's just not fun. The game doesn't get good until heavensward.

Not native, but Guild Wars 2 runs great on Linux and is a whole lotta fun

Also, in my experience, proton runs most things just as well if not better than native Linux games.

Veloren 🫣

How about Runescape

Project Gorgon!

Not native but Palia is one that recently released and is getting a ton of love. It runs on Linux using lutris-GE-Proton8-13

Not really a mmorpg, but you really should try Baldur's gate 3, runs great on linux

I'm one of the 5 poor sobs who still plays darkorbit, and someone on github made a linux native launcher available as an appimage. I don't recommend playing it though, because aside from the community becoming smaller and smaller, the game also runs like ass even on a high end system (not because of the unofficial app, but because of the game itself), and it has this issue with it taking up more and more ram over time, and it has been like that for over a decade now. Also a lot of server issues lately. The devs don't seem very interested in improving the game.

I have played at least Albion Online and Wakfu that run natively without any trouble, and work quite great. Lots of other run quite great using Steam compatibility layer or Lutris.

I've played several on Ubuntu and do agree that Albion and Guild Wars 2 both play great and are a lot of fun

https://store.steampowered.com/app/761890/Albion_Online/

Can't really recommend it though, but it seems to be pretty popular.

I mean... good chance just about any of them will work on linux, with pretty minimal effort.

I used to play WoW on linux, back in 2008/2009, without issues....

Not sure how good it is but Ryzom is Linux native and open source. I'll be checking it out soon

I spent a lot of time playing The Mana World when I was younger

ESO runs great using Proton

FF14 works great with Proton. I would still advise to use XIVLauncher, as it is better in every way to the official launcher.