Ask HN: How does FB advertise a niche game I'm playing to my friends?

I'm currently playing some niche game and I've talked about it with one of my friends recently (not on Facebook, but Discord). The game has a web site, which I will frequent with my machine. It requires registration, but I use a different email for it than my Facebook account. For the record, I also rarely use Facebook (~1/month type of situation).

My friend now showed me a picture of an ad on Facebook for the same game. This doesn't feel coincidental as the game is very niche and is fairly old/stable. How did Facebook do this? Can the game just go on Facebook and buy ads for people who are friends with the game's players? If so, how would Facebook know that I'm a player? Browser fingerprinting despite adblock/socialblock? IP tracking?

This feels super creepy. I'm aware of some of the best practices for ensuring privacy on the internet, but the measures tend to become a trade off between privacy and convenience, which the latter tend to win. Are there some more basics things I can do to protect myself from this type of problems beyond just having Ublock Origin with social blocklists, logging out of Facebook/using Firefox container tabs, and potentially VPN?