Still great game, love having the Definitive Editions on GOG.

One Problem is, I can only play it Windowed. Full Screen game will crash no matter the resolution.

Second Problem is, achievements are definitely not all working properly. At least "On the trail" and "Car chief number one" are not unlocking.

The achievements unlocked for me as i have both on the trail and car thief number one registered as gotten.
And i played the game fullscreen without problems. Though i think i had turn off disable Full Screen Optimizations for game exe
And maybe i got the achievements because on the game exe i also used run as admin and simply ran the game through gog galaxy.
My resolution was 1920x1080

I also started the game through gog galaxy. Played with WQHD. I think that already was a problem on my old PC, where the game ran, but not in full screen. But will try again.

My first play playthrough, which was feb. 2024, I got a lot of the achievements, but not all. This time I got all five postcard cars, but I didn't get one of the two achievements :-(. Not that important to me, but would have been nice to have.

So you are starting your whole gog galaxy as admin or just the game? Didn't have to do that to get the other achievements that I got with my first playthrough.

I am using admin on the mafia game exe and not galaxy

Thanks for the tip, but sadly doesn't change anything. Launcher says it's fullscreen, game starts windowed. As soon as you change to fullscreen in game, it changes to fullscreen and then freezes instantly.

And, after running the game as admin, drove all five postcard cars, but didn't do anything either.

Playthroughs done, will continue with Mafia 2, but thanks again.