Weird, I was just checking Lemmy randomly and crossed this. I don’t have an answer, but I stream EverQuest and know many players use Linux. If any community can help you, it would be the P99 forums or the Project Quarm discord tech support. Between the two communities, you have a couple thousand players with decades of experience. Might even be worth checking out The Al Kabor Project’s discord as well.
I doubt you’ll find these two niches intersect anywhere else.
Edit: I did successfully get it running on my Steam Deck, which uses Proton, so I know that might be a path worth pursuing. Find one of those guides and see what you can get to work.