You can talk about the project organically here on related posts and hope people jump on it. Do this on related subreddits too. It's not blatant advertisements, just find a way to incorporate your game into conversations.

Or, you could do direct advertisements on social media platforms. It will cost you, though. If you have some money, you can go this route while still doing the first one too.

Directly reach out to game devs. Email, LinkedIn, you name it. Ask what they think of it.

I think if you solve a real problem there is no way you don't already know some users. Otherwise how do you know you build something worth anyone's attention?