Question for puzzle game developers

I've been developing a mobile game called Jigsaw Solitaire: Card Puzzle, and while building it I kept running into an interesting design question.

How do you balance difficulty progression in a puzzle game so that it stays challenging without becoming frustrating?

I've experimented with:

• Gradually increasing puzzle complexity.
• Introducing new mechanics over time instead of all at once.
• Rewarding strategy instead of trial and error.

I'm curious how other developers approach this problem.

What techniques or systems have worked well in your puzzle games?

I'd love to hear your experience and learn from the community.

Link : https://play.google.com/store/apps/details?id=com.blacat.jigsaw.solitaire.puzzle.master