This is not an answer that addresses any game, or game mechanics, because I do not think it is very relevant in this situation. The scope of this question goes beyond being a GM or player problem, for that matter.
As someone with a real life degree in Clinical Psychology (2013, BSc), being a part-time teacher who frequently deals with students with ADD and ADHD, and a boyfriend of someone with ADD, I'm not sure if This platform is the right place to find the most complete, or most important: the most effective, treatment. If you are serious about taking "ownership of your condition", which is really great and admirable, I can recommend that you seek professional guidance. Talk to your general practitioner and ask if you can see a therapist who specializes in your condition. I suggest this, because in general people seem to underestimate the difficulties of conditions such as ADHD.
There are several ways to deal with a deficit of attention. A qualified therapist is trained to offer (personalized) advice and / or guide you in the search for your own ways of dealing with your attention span. This way you can find "tricks" that can also help you at the table. Of course, the actual quality of mental health care varies greatly by country. So, if that does not work, or does not fit your personal needs: some of my close friends have to deal with ADD every day (similar condition but without hyperactive tendencies). They discovered that "alternative" treatments can work really well to maintain better concentration, such as mindfulness, meditation and / or yoga.
- Note 1, about the second-hand experience: Keep in mind that meditation in itself is primarily an exercise in observation, while postponing reactions, both emotional and physical. That canHowever, they also have religious intentions or connotations. If you do not want that, I can recommend Vipassana meditation. After having read the book and having a girlfriend with ADD who did the course several times, I can say that this type of meditation welcomes all nationalities and religions.
- Note 2, about the second-hand experience:
Both my brother and a friend, both coincidentally playing in a D & D 5e game that I am GM, also used to have attention deficit. After seeing their general practitioner for a while, and some tests later, they discovered that they had sleep apnea. After this diagnosis, they took the necessary measures to deal with this sleep disorder, and since then their attention is much better! This emphasizes my point with regard to seeking professional help.
In any case, talk to your friends. Explain that "just paying more attention" does not work for you and that you are taking steps to make it work. From a personal point of view, I would like to end with: taking "ownership" requires time and effort. Having a table that understands that helps a lot. If your attitude is: fix this now or go away, I come to the conclusion that you are not friends at all and you find a game with more concerned people. Good luck!