Hail everyone, sorry for the super late reply, life has been hitting us hard with a number of curveballs lately and we're trying to stabilize the entire situation before being able to return to our normal routine. It's been super stressful to say the least, but we're hanging in there. Anyway, in addition to what Gambi said, which is what I can confirm works just fine with Steam + Proton, you can also do the automated installation method of EQ2Map. I'll have to retest with Proton 9 on my openSUSE / Ubuntu machines to make sure, but IIRC last time I tested I decided to use an app called "Protontricks" (available in Ubuntu's software center or generally
available via Flathub / Flatpak - depends on your distro). I used Protontricks to install the EQ2Map EXE into the existing EQ2 Proton prefix and after that I used Protontricks to install a specific .NET version etc. into the same prefix in order to make the EQ2Map interface show up correctly for the automated version. After that, you go into Steam and change the launch EXE from your installed EQ2 entry to the EQ2Map launcher thingy and you're all set. That's what I remember doing last time, but I'll have to recheck just to make sure.
I know this method works like a charm with Crossover and EQ2+EQ2Map:
EQ2MAP on Ubuntu 22.04 + Crossover 23
I'll try to retest with Steam + Proton and report back asap. Meanwhile, I hope the above helps point you into the right direction.
+1 I also vote for official Linux acknowledgement or even official support of any kind. Windows 7 is still supported, even though it's "officially" dead, and Linux does have higher gaming numbers to boast after all (statistically speaking). I'm actually quite surprised by how many of us use Linux around here. I've had ppl contact me on Steam seeking help with EQ2Maps etc. after switching to Linux recently, and it seems we have even more folks lurking in the background using Linux for all things Everquest too. Looking good!