GOG Galaxy is an optional launcher, not a sales platform. That is GOG.
GOG is not a suitable sales platform as Vintage Story requires a login for playing and that is frowned upon by users of GOG. Also you will have to provide functional offline installer for Vintage Story which would have to function without any login.
See also the GOG Hitman disaster: https://kotaku.com/hitman-goty-edition-removed-from-gog-over-online-drm-1847833140
On GOG it is expected that you buy the game and play it without any checks or logins to (from the perspective of a GOG customer) a 3rd party login. In the worst case, that also could spell doom to Vintage Story itself, as such a backlash will occur onto the game as long as the login is mandatory.
( personally, I don't mind the login in the game )