Video games can get pretty finicky when you go off the beaten path, requiring a lot of extra "mechanical skill" to get right.
A certain glitch on a game I play involves carefully timed button presses while keeping the control stick in a specific, narrow range just outside the "deadzone". You then go fast, and backwards, and have to steer by switching which side you're holding the control stick on. If at any point you go out of that range (either through the center/deadzone or tilted too far), it instantly stops working. And some other tricks in that game are hard.
So that sounds like a good way to practice some dexterity, I know it's helped mine.
Other than that there's stuff like Rubik's cubes, arts and crafts,