Thinking about taking up martial arts (again)

My self-discipline has been crap lately. My therapist thinks I have ADHD. I spend all my time in front of a screen. I don't exercise as much as I used to, I bounce in and out of the gym, and I haven't been out dancing in years because - while I'm not the most covid conscious - that many people in a confined space together gives me the heebie jeebies nowadays.

I need something to right the ship. I did Korean martial arts when I was a kid but I never practiced on my own and was too much of a goofball to take it seriously.

I need do something that requires enough concentration to get me out of my head and ideally involves some speed. Any thoughts on what's good? Things that worked for you?