I'm all for releasing a native Linux build on GOG, but GOG is still not treating Linux as a first-class platform. There's currently over 33k votes for a Linux client on GOG's wishlist but there's still no actual Linux support. We need GOG to release their API (not really the Galaxy client, that's optional) for Linux, otherwise it's not possible to provide a feature-complete Linux build on GOG and we don't want to officially release a version that is missing some functionality like multiplayer.
Until GOG provides first-class Linux support, I can only recommend the native Linux version on Steam or unofficial methods of running the GOG version such as Lutris/Proton/Wine. Meanwhile I encourage everyone to let GOG know that a Linux release of the API is desired!