Making and finishing small games is probably the best way to learn, and game jams are a good way to get yourself to finish small games, if you have trouble doing it on your own. Working under a strict time constraint forces you to scope way down and just power through it. Finishing is a skill and jams are great practice at it. There are jams that run for all different durations, and in most of them you can absolutely work alone, if you prefer. I always work alone, and I've done jams ranging from one week to two months.
I do think that you will get more out of a jam if you are at least passingly comfortable with your tools before you start. Otherwise, you may spend a lot of time just trying to figure out how to perform unfamiliar tasks, which could be frustrating. Still, you won't lose anything by trying. Even if you don't finish by the deadline, you've still learned something, and you can still finish the project afterwards, if you want. Some jams and jam communities like My First Game Jam are explicitly beginner-friendly and might be a good place to learn.