Honestly, while big jams like this are fun and rewarding, I also enjoy just joining small jams as well in between them. It let's you get some good practice in a low stress environment where there's no pressure on yourself and you can focus on learning and improving.
My first big jam was the Miz Jam 1 this summer, and I thought it had a pretty cool gimmick where everyone uses the same asset pack, and the rest is open ended. It also had the really nice feature where you had 48 hours you could spend however you wanted over 9 days, so it was a lot more manageable if you had other things you were busy with as well. I believe that the next one happens this summer!
But honestly just look through the jams on itch and if any one has a gimmick that you like, go for it! (There's an MS paint jam that I've been trying lmao)