DRM Free doesn’t magically make it run natively on another OS, it still needs to be manually ported. No, there’s only a Windows version, but the Windows game will run perfectly fine on Linux under Wine/Proton if you use the Heroic Games Launcher for your GOG games.
I am pleasantly surprised to find out that I’ve only spent $559 (356 USD) since joining Steam in 2016. Especially since I’m GOG only now.
“Absolute legend” is is just an Aussie saying. Nothing bad about it. Calling someone a legend is very common in lots of parts of Australia.
I really appreciate when a dev puts the extra effort in to make a Linux port, but I can understand when a solo dev such as you doesn’t have much time to spend on porting. To be honest, I’m just happy if the developers at the very least test the game on Linux using Proton and WINE to make sure it’s working well and correctly. That way if making a native port really is that much of a hassle, I expect them to at least test it on Linux. I think that most large teams should make a (good) native port, though.
I don’t know who said that but that is not at all how DRM works. If the developer does not explicitly release a Linux port of the game, it will not run natively. After all, the offline installer files for Windows games on GOG (when you aren’t using a launcher) are .exe files, which will only work on Linux using the WINE compatibility layer, which automatically makes it not native.
Also, have a look at this screenshot from the actual GOG store page if you’re still not sure:
It only shows a Windows icon, this is how you know what platforms it runs natively on. If there were a Linux port, there would be a Tux penguin icon to the right of the Windows icon. For example: