I used to be a big fan of Sid Meier's Civilization, and I bought the Civilization board game (Civilization: A New Dawn.) It turned out to be trash, and I regret buying it. That was when I discovered that just because a game is good it doesn't mean its spinoffs are always good too. I'm just relieved I didn't buy the Minecraft card game too. I did buy a couple of Pokemon TCG decks though, and that game was pretty fun. Another thing I regret about Civilization is buying the first Civilization VI DLC, Rise and Fall. I didn't like it and thought it made the game too complicated.
I also regret creating a survival world on Minecraft Windows 10 Edition. There was a point in time when Mojang handed out free keys for Windows 10 Edition to all players who owned Java Edition and I recieved one of these keys. At the time, I was convinced Mojang was going to abandon Java Edition and the future was Bedrock Edition, whether I liked it or not. So I started investing a lot more time in Bedrock Edition than Java Edition and created a survival world on there which I built a lot of things on. In the end, Java Edition was not discontinued and I still preferred playing on Java. Bedrock Edition sometimes crashed randomly, its interface was slow and Bedrock servers sucked. Java had none of these problems. I'm now mainly back on Java, but I still need Windows 10 Edition installed because of that one survival world. It can't be transferred to Java Edition and I don't want to delete it and lose all my progress, so now I'm forced to tolerate Bedrock Edition every time I want to play on one of my favourite worlds.