The good thing about this time of year is advent: a time when people do something every day from 1st to 24th or 25th December. And it's the same with coding challenges: you get one per day for 24/25 days.
Here are a few that I'm doing this year/have done in the past/will do in the future. It's not too late to start any of these! You might just have to do more than one a day to catch up, or just skip the first few.
This is one that can be done in any language. It's also not easy. I started this last year, but only did a few days before the difficulty level rose above the amount of time I had available.
I've lumped these together because they're from the same people. You get a Figma design (for the CSS challenge) and instructions on what you should do. You can do just the CSS or just the JS, but both feels more satisfying. I haven't started this because I just don't have the time yet, but it looks fun, so I've been saving the files and will do them when things have quietened down - maybe one a weekend.
Anyone know of any more coding advent challenges?