Pine Studio have put the Native Linux version of Escape Simulator back up, but they're still recommending you use Proton. Back in late May I wrote about how they completely removed the Linux version, noting that they were seeing too many issues with it with Proton being more reliable for them.
In their news post they've now updated it to note:
We just released a new update that brings back the native Linux build (v35497).
We're still waiting for Steam to approve our Proton version of the game and after that we'll default to that version of the game. We strongly recommend Steam Deck/Linux players use Proton (specifically the Proton Hotfix version), as it offers better stability and performance for most setups.
Seems they didn't fully think it through. For one, the Native Linux version is what Valve picked for it to be Steam Deck Verified, resulting in install failures since the update. When they say they're waiting for Valve to "approve our Proton version", they actually mean they're waiting for Valve to re-do the Steam Deck verification.
Additionally, I'll put my own note here that a developer recommending Proton Hotfix is a bad call, since that's only meant for very specific titles and isn't updated often. When it is updated for the next time a major release needs it, the changes between the two versions will be pretty big which could then cause other problems.
Regardless of any Native versus Proton arguments, I certainly don't blame a developer wanting to provide the best possible experience, but I do think entirely removing a version people paid for is not the way to go about it. What it does is highlight a flaw in how Valve handle Proton, giving developers directly no choice on if it's default or not. If developers were able to officially tag Proton as supported and default, it would certainly help.