I believe that Everybody Codes has a leaderboard where it starts counting from when you first open the puzzle. So if you're looking for coding puzzles with a leaderboard that one would be fair for you.
I hate when I buy an interesting math book and then it's like "oh wait, no solutions." And then I end up going on GitHub hoping for community-worked solutions.
I've been wanting to read books like Algorithms for Optimization (https://www.amazon.com/gp/product/0262039427/) and Probabilistic Machine Learning (https://www.amazon.com/gp/product/0262046822/) but when I open them up I immediately think "wow I really need to refresh my calculus because I have no idea what's going on." It sounds like I should look into Math Academy for relearning old Calculus and learning some new stuff as well.
I think I would enjoy working for a 3 letter agency but the USDS website makes it look like you'll be working on very different types of things. Although I suppose they wouldn't be advertising that work.
https://everybody.codes/events