Recently I made a board game based on my favorite game, Foxhole, and made it in tabletop simulator. I shared this with other people I play foxhole with and the foxhole community and they really liked it, some loved it. I've already reached that milestone though with my first game, although there is at least 5x the people playing this game already. The milestone is people playing it without me prompting them/sharing it with them. I woke up one day and saw 2 people playing it, without me ever prompting them to do so. It blew my mind when I realized it and I'm still happy about it.
Now the next milestone I can think of is gonna be to get someone pays for a game I make, either by donation or buying.