For me it was minesweeper clones. I got frustrated one day and decided to learn how to be good at minesweeper. After beating the medium and large boards a couple times I looked on Steam for minesweeper versions, and turns out there’s a whole genre of clones. Some of them are direct clones of the game, while others are very heavily inspired by minesweeper. The two best I played were Hexcells and Tametsi. Hexcells is stylish and is only hexagons (as opposed to the minesweeper squares), while Tametsi has squares, rectangles, and hexagons and is a lot more barebones. However I found Tametsi to be much harder. There were some levels on there that took me an entire day, and I think there’s like 500 levels. 150 levels
Damn Paradox strategy games. I still had CK2 laying around on my disk, back from when they gave it away for free, and one day I decided to learn the game. Fast forward a handful of games and I just bought CK3 and am playing every evening.