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.
When I was stuck in bed for 2 months straight in 2014 from a broken neck, I got a couple of Sudoku books and did every puzzle in the books. Now I just play Open Sudoku on my phone. Ever since then I kinda measure my pain/mental/overall sleep quality state by checking how fast I can solve the hardest puzzles that have real solutions without guessing. Anything over 5 minutes is bad for me.
I started watching cracking the cryptic’s sudoku videos a few years ago, and have been addicted to variant sudoku since.