Ok I was banging my head against a wall trying to figure out why a fresh totally clean installation of Kingmaker was crashing. Until I thought to try launch from Galaxy.
Which WORKED!
WHY??
I thought part of the point of GoG was NOT having to have something like Galaxy running or DRM like stuff running?

So why can't I launch Kingmaker OR Pillars of Eternity 2 from their executable and can ONLY run them from Galaxy?

YES I am using mods.

NO?YES? - the problem occurs even without MODs.

The logfile is truncated and does not show any errors for the crash

I've heard of games that won't work without GOG Galaxy if they detect it's installed. This may be one of those cases. Support or the general forum might be better places to look for help.

In any case, GOG Galaxy isn't DRM since you're free to start it up and launch your games with no Internet connection.

I know it is not really DRM, but I feel like requiring Galaxy is a bit of a problem too though.

It's not required. If a game won't work without it, that's a mistake. Open a support ticket if you haven't already.

I have the same problem with Kingdom Come Deliverance I. I'm writing my solution for future questions here. TLDR: There is always a shortcut writing "Launch [xxx game]" at the game root directory which is always that folder having the name of the game. You can just launch the game here. And you can copy the shortcut to the desktop.

The Galaxy version executable has no DRM. IMAO the reason the game failed to launch via double-click is that some executables may need a configuration file or special launching setting. In my case I found out that launching the executable via administrator mode works.