You can look at competitive programming sites, they are a lot more serious than leetcode/hackerrank

https://dmoj.ca/problems/?type=5&show_types=1&order=-points

https://codeforces.com/problemset?order=BY_RATING_DESC&tags=...

Hackerrank has some fairly no-joke problems on it. Is https://www.hackerrank.com/challenges/decibinary-numbers/pro... too easy? I enjoyed that one a while back.

I think I have a list of curated DP problems bookmarked somewhere, I'll see if I can track it down.

Energy markets used to use Lagrangian Relaxation and Dynamic Programming to find the least cost dispatch. Some still do, but the larger ones (all the ones in the US) use Mixed-Integer Linear Programming and Linear Programming as the engines can handle a lot more and still solve.

The problem is that you'd need to get your hands on a large dataset and none of the true ones are public. I think some of the national labs have synthetic models of various sizes to play with. Seriously cool field.