I think creating a simple programming language that supports recursion is a good way to get better.

I did so in one of my side projects that I have recently released as an iOS and macOS puzzle game named "Recursive" where recursion plays a central role and allows solving levels with very short programs [0].

Also, I may be biased, but I think that players can improve their mastery of recursion using the game.

If you'd like you can contact me and I will gladly send you a promo code (contact email at website).

[0] https://www.kidori.com/games/recursive/

(edited to fix typos)