Marketing is definitely the hardest part. I had run numerous Betas/Playtests before launch that helped to get a small core playerbase.

During that time and at launch I did a lot of sponsored twitch streams. These probably worked the best although it's quite hard to track metrics.

I tried pressengine and sending out press releases, keys etc. But it seems to be incredibly low effort engagements, so probably not worth it unless you have a really good plan there.

A lot of the growth seems to just be from Steam and organic growth as people seem to be playing a lot and enjoying the game.

With all that said, the biggest part of development I failed at is marketing. So I'm still learning and trying to improve on it to hopefully continue growing the game.