Not FOSS but free2play and native with vulkan:
https://store.steampowered.com/app/884660/CRSED_FOAD/
Palia is fun for awhile but not a lot of lasting content there yet.
An oldschool style Linux native MMO I still recommend is Project Gorgon. It’s a very social game, while you can do a lot solo eventually you’ll run into the game’s only real punishment which is dying from a boss fight. You’ll get a permanent curse that can only be lifted by defeating that boss and the best way to do that is to find other players in game to help you do it.
Looks like there is a bug that makes this game unstable on some kernels (like in default Ubuntu):
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2034718
Same, our battle just to get a foothold on Ashlands was pretty epic but now we’ve taken down a fortress and things are getting a lot easier.