https://adventofcode.com/2023/
It's a pretty good, progressive challenge from day to day, the goal is to complete the puzzle and provide the solution, and you can approach the puzzle however you like.
I take the approach of using programming, but recently I have more fun throwing the challenge into ChatGPT to see if it can generate the code for me, usually it cannot generate the answer directly because sometimes the puzzle requires iterating over a data set that it doesn't enjoy taking at all at once.
It managed reasonably well with day 1, but the second part of day one took a lot more massaging for it to understand what I'm asking of it - apparently it's possible, but I guess I can't quite massage it right with the correct prompt.
For a more 'cyber security' approach there's tryhackme: https://tryhackme.com/r/christmas which is also fun :D
You can also setup a leaderboard for adventofcode, just for fun we could have a community one? 
