I play Valheim on Linux and have hosted a server before.

Easiest way is just to use R2 Mod Manager. It's available for Linux too. You just launch the game through it instead of Steam / wherever you launch it. I use PikaOS now which is based on Debian but had Bazzite in the past and it worked there too.

You do have to tell it where Steam / the game is installed though, but that's true of it even in Windows.

PS: fastest way to get help is probably venting/ saying something isn't working in a Linux community lol. It's a useful thing to know. That's how I sometimes get my answers too.

environment variables are a thing on windows as well. I grew up with windows and had to set environment variables for random stuff there as well. That is just a (depending on what you do) fairly normal thing. i hate to say it because obviously we all want people to switch to linux and have a good time and want to be helpful but … that’s just a skill issue

Well that would depend on what you use to run that mod manager, as that's probably a Windows application using wine (or proton, which is still based on wine). If you always just launch it from bash, .bashrc is the easiest. Launchers like Bottles or Steam will let you configure launch options per program/game. e.g ENVVAR=value %command% (%command% is a standin for the actual launch command, you leave that as is - it's necessary because you can add things both before and after the command)

But yes, overall, running Windows software is still the most annoying part of using Linux. At least usually for games run from Steam there's not much tinkering needed assuming the game works (so no kernel level anticheat games)