How to force the game into windowed mode?

I have that DirectX error poping up when I try to launch the game.

I found that if I keep the game unfocused, which keeps the game in windowed mode, it runs fine. As soon as I click on it the games goes into fullscreen and crashes immediately.

I can't go in the game options and change it to windowed (or borderless windowed) and the config file looks like it cannot be edited outside the game. Geforce Experience can't 'optimize' it either.

Any ideas what I can do? maybe a launch option?