First of all, gratz for your game, really an awesome work.
Second and totally off topic, why publish here and not on any major platform like Steam / Epic ? Wouldn't the reach your game get compensate taxes ? Aspiring game dev here.
I thought of myself first, of course ;-)
I had forgotten that Railbound is a Unity game younger than 2015. The last Unity game I know that works on my system is made with Unity 5.1.
But there are probably other gamers who, like me, buy games exclusively at GOG; I buy games using Paysafacard, which is only possible at GOG.
I hadn't seen the game on GOG yet which is probably because I ignore Windows games that cost more than 10 Euros. The probability that Windows games will work for me is not very high and I don't want to give away too much money. I use MX-15 Debian Jessie 32 bit and Wine 1.6.2-20, sometimes Wine 1.8.1.
Not all people are Polish ;-)
1. People don't like DRM
2. You don't actually get that much more reach from Steam and Epic. This isn't the early 2010s where simply publishing on Steam was guaranteed to make an indie game more successful. There is so much on the platforms that many users will simply never see, or outright ignore, a lot of games.