Don't accuse them of being ADHD, or insist too strongly
If you do bring it up, I would say make sure to really emphasize that you don't think they need fixing. It's something that might help them overcome their own struggles, not something to make them a better person for others, you know?
Everything I am really good at, I am really bad at, depending on context and the wobbly compass that governs my internal motivation.
It is definitely not all bad. Without my hyperfocus, my life would be unrecognizable. I would be unrecognizable. Hyperfocus is core to so many things I am good at, care about, and have achieved.
My ever optimistic self would fail and fail and fail, create a system, fail, create another system, fail, .... at seemingly easy things.
As soon as I had a rational reason for otherwise inexplicable challenges, enormous amounts of stress evaporated.
Now I know what things are a lost cause: So I get help, delegate, find another way. Being bad at something, and recognizing it, is not the same as failing.