You didn’t come up with the name and it’s perfectly realistic to imagine more than 1 person coming up with a similar idea based on the same concept. Even if someone “stole” your idea - do it better than them and you’ll have nothing to worry about. I’d be more understanding of your concern if a big AAA studio happened to make this release so close to yours, but even then not much you can do due to aforementioned reasons. And while Steam lets you use any name you want, even if it’s already taken, it will put your game first on the search list if more people interact with it, which will naturally happen if your game is good.