[D] Leetcode-like puzzles but for Machine Learning

Are the resources with short (but not easy) ML puzzles, similar to algorithmic puzzles, that are on leetcode/hackerrank etc? By short, I mean something different from "Here the batch of data. Build the model, that will give the best predictions on a test set", because they rather steal your time, than helping you to improve your machine learning thinking.

As examples of such problems, I can mention developing some custom loss functions (different from the common MSE or CE), developing …

leetcode machine machine learning machinelearning