I'm looking for a method that allows me to study Marxism without losing focus, without losing memory, and in a way where I'll actually internalize what I've studied about Marxism.

Go to meetings. My local DSA has reading and discussion groups that meet monthly, that would be a good way to go. Interaction helps a lot. I obviously dont know where you live and what your group is like, but mine is full of everyone from anarchists to Trotskyists.

What if I can't go to meetings? What about in my bedroom? What about Discord servers?

I dont use discord so 🤷‍♂️ you asked "what do you use"

Tbh, most people get way too focused on theory, a fairly basic understanding is all you really need. What's more important is participating in organizing workers via direct actions like mutual aid.

Past a certain point communism is more about what you do, not what you think. The world has changed quite a bit since the last successful revolution. The next one will likely be shaped to meet the material needs of the day and the theory that will develop from that has yet to be written.