I was late to the party for Advent of Code. But, as it turns out, Advent of Code is fantastic for learning a new programming language, tools, styles, and so on, due to the low floor (just get the right answer) and high self-imposed ceiling (how can I make my working solution better?). This is high praise coming from a person who doesn't enjoy obscure riddles, or puzzles that are stereotypical of "programming puzzles".
Advent of Code happens to be in the "Goldilocks zone" of interesting enough to be fun, but not so hard as to be discouraging (at least for the early problems). It is way, way less intimidating than tackling a fully-fledged project in a new language.
For the 2020 problems, I'm using it to learn Clojure, alongside my daily staple, Python.
I have no hard intentions to finish every problem, nor to work on a problem every day. This is just a little bit of fun to see how far I can get!