The website nobsgames.stavros.io helps surface these, and let’s you filter out based on different things.

One that I like in particular is Gauguin. It’s a Sudoku-like with different math-y rules.

Anuto TD is also really good, but not so low stress.

Lichess, if you’re into Chess. It’s a great, no compromise, high quality app. Stressful if you get too worked up about competitive, but puzzles are at least relaxing.