Gaming on Linux is hard because there's not one Linux, there's tons of Linuses. What version of the glibc/libstdc++/mesa/xorg/wayland/kernel/drivers are you running?
The Linux ecosystem is fragmented in such a way that only open-source and an army of volunteers can really work around. It is really not binary-friendly at a fundamental, philosophical level.
(You're not going to get game companies to open-source their games, except as an exception, and after their economic life is finished)
The Steam Deck provides one well-known hardware and software platform that a vendor can reasonably target. Don't expect much more except by the most dedicated developer.
As of right now, proton and proton-ge both build in and require Steam Runtime Version 3 to run in. The steam client itself is running in a runtime, and I think it is the scout runtime, so LD_PRELOAD based. This means that steam has its own common platform to "deploy" against, and all Linux native games have a common platform to deploy against.
It used to be that games had to be compiled in a chroot for Steam runtime 1.0, but now with Steam runtime 3.0, developers are heavily recommended to build their game in a "OCI-based container framework"—so podman basically—and enable the Steam Runtime 3.0 on steam. I know that TF2 and Dota 2 use steam runtime 3.0, and apparently so does Retroarch. Of course, since there is a podman/docker image, you can also test existing games to see if they run in the runtime too.
You can find a lot of more information about the steam runtime 3.0 here: https://gitlab.steamos.cloud/steamrt/sniper/sdk
Valve has a gitlab with lots of great docs for developers who want to publish a linux native game.
I think all native linux games will run in the Scout 1.0 runtime by default
Edit: I will say that as an end-user, running an up-to-date Linux kernel and Mesa stack is important for gaming. I know some people who run Mint and are surprised that their Radeon RX 9060 runs like ass. As long as you aren't using a Debian based LTS distro, like mint or ubuntu lts, or you are running those distro but get a newer kernel, you should be fine. This matters less for older hardware, but having a newer kernel and especially a newer mesa version is important.
The alternative is using (what is effectively) a cross compiling toolchain to target Linux from itself! Or spin up an ancient Debian image (including ancient compiler) to build against ancient glibc.
It's hard to blame anyone for just using Proton, with the perma-stable Win32 API. No build containers, no chroot, no locking the build to Steam. Just the same build infra you already have.
One could argue that Proton is a kind of a container. It has a runtime system, filesystem, wine itself has several executables and interprocess communication, etc.
(Not saying mesa should be statically linked, but that we should be able to load and use it without libc)
That's irrelevant, because Proton is literally a Windows emulation layer, (the product of decades of cumulative work). "they" (Larian) didn't have to do anything for that.
Certainly Larian's effort for making a Steam Deck native version is commendable (I hear it was the result of one single employee's effort). Larian is a rare beacon in the video games industry biz for the amount of post-launch support and content they provide.
But my point remains: supporting Linux broadly is a far larger, and ultimately unreasonable, ask, than just supporting the Steam Deck.
