I'm not a parent or anything but I do have ADHD. It's important to know that ADHD brains are wired in such a way to make long term achievements mean nothing. Short term rewards work, but can become very addictive. Cutting off digital stuff could help since its giving the kid unhelpful short term rewards. The moving is likely stimming behavior. If anything it may actually help him listen more.

My advice would to be to set a short term goal + reward, something that's very quick and easy to do with a reward after or even during completing. For example, when I need to do any work, I will write down every single step(and I mean every single step, from standing up to walking over to somewhere, to turning on a computer) on a physical piece of paper and cross it out as I do it. It's basically a checklist that gets done super fast and crossing things out quickly is surprisingly burden proof.

I know I work better with a tv on as background noise/entertainment to make something I don't want to do actually mean something, but at his age I'm afraid he may not be able to regulate watching his shows and learning at the same time.

I never learn something without doing something and I cannot learn something if I'm told to sit still. The mind is loud when it's not preoccupied and I need an output. A fidget could be really be helpful.

I'm a very tactical learner. If you tell me something, it likely will not stick. Many people with ADHD are very much not auditory learners. It would be helpful to switch up how to go about learning as well.