Gonna test this and get back to you. I do know the windows version works well through proton,
EDIT:
I was unable to reproduce, I tested on the latest Pop!os and the latest Ubuntu. Ubuntu failed, and it seems to be because Ubuntu has dropped support for 32-bit executables. From my research, Linux Mint is based on Ubuntu, so it likely has the same issue. I'm going to see if I can put together a 64-bit build. Might take a couple days, but I'll update you when I have it.
I've finished reviewing my options, and I am unable to build a 64-bit exe for you in a reasonable timeframe. Unfortunately, Linux Mint has just dropped support for games this old, and although I want to continue porting it up and supporting it, the engine I used for it, Unity3D, has also dropped support for the language is was programmed in, as well as the engine version it used, meaning the current game is completely locked from further development, including the ability to produce builds. I can't even open the game now in Unity, unless I pay a minimum fee of $200/month or come to a backroom deal for this specific version. Sadly I can't do that.
I was in the process of porting the game when that unity thing happened, so had to drop that port. At some point I will be bringing it to Godot (probably), which will remove this risk entirely. I'm sorry to say I am unable to fix your issue. My suggestion is to download the windows version from this page, add it as a non-steam game in steam, and run it through the proton runtime, which should work on your device. It's a big of a 'is this supported or not??' edgecase, where proton works fine on linux mint, even though 32-bit executables do not. The easier way to do the same without steam is the Heroic Games Launcher.
I will be adding a note to the store page for future players.
