Consider trying last year's advent of code -- I think they are fun puzzles, and in my opinion, a programmer able to deal with logically complex requirements should be able to solve them all.

I've been a professional programmer for a long time. My opinion is that what we mostly do is more akin to plumbing than "engineering". When we say "complex" we mean DAGs, CI/CD pipelines, a self-healing K8s setups, and so on. But this stuff -- at least in my opinion -- just isn't very hard, not in the way that a fancy video game, a robotics control system or a sophisticated compiler can be.

Computer science and mathematics applied to coding and internalised in your practice will not merely make you a better developer, it will put you on another level; you won't see code the same ever again.

Finally, I'd suggest that solving puzzles is more indicative of what you already know rather than a good way to acquire new knowledge.