Helping an ADHD player as an ADHD DM

Hey y'all, I'm not sure if this is the right place for this post, but here's the situation.

I have ADHD, as well as 4 of my players between the 2 groups I run. As a result, my games tend to have a lot of tangents and side conversations. Thankfully I've gotten pretty good at getting people back on track.

Well, except for one player. I'll call him Steve for the sake of anonymity.

Steve is a very good role player and most of the time I enjoy playing with him. The problem is that I can't keep him on track for the life of me. I'm trying to be patient with him because I know how difficult it can be to play TTRPGs with ADHD, but we've been playing for almost 2 years in some capacity and I've reached a point where I don't know what to do to help him play the game with us. I'm summarizing the combat for him every time his turn comes up, he hasn't learned the basics of his character or the game as a whole, and now that we're playing in person he won't even stay at the table half of the time. I want to be accommodating, but I don't know how.

Any help would be appreciated, thanks!