Any idea how to run the game in window mode?

I can't even minimize it or use other screen in any way :/

ok, DXWnd was the solution :) Just enable 'run in window', 'emulate win maximize', 'recover screen mode', 'cursor visibility: hide' and it works quite fine :)

I will necro this to let all know, that with one of the latest updates, GoG added custom direct x wrapper, that allows you to set game to run in window (you can even select resolution of this window).

That's good to know, Sulibor. Thank you.