OK So I guess for now I'll stick with trying to get the windows version working with proton. It could be as simple as using 127.0.0.1 internally as the loopback address instead of 255.255.255.255, which is currently hard coded, so I'll try once I get set up. I'll have to see about installing proton on my desktop (although I'm by no means a linux expert, so adventures ahoy!) 😅 Thanks for digging out the user path, I had a feeling proton was going to do something like that when emulating the user dir of a windows system, so that's useful to know.
I did modify the rpath of the linux bin to point to the included lib folder, specifically because libraries like bullet are so varied between distros, but the fact that arch/ubuntu-debian are so different that it doesn't work doesn't surprise me all that much. It's a shame that linux distros are just so fragmented - it puts me off spending more time with the platform.
AppImage looks promising, especially if I can hook it up to the cmake script. I've still got a big chunk of work to do to get the next update to VGA Golf done, but after that I shall definitely be looking into this more. Oh, and you didn't hear it here, but there may be a chance of the game coming to steam in the future 😉 Potentially this could make things a little simpler when running on steam deck, if only because it'll be ported to Valve's networking libraries.
Thanks again for the help and feedback, it's really appreciated!