As someone with ADHD, I think the best way for me to compare them is that hyper - focus is more like "uncontrolled - obsessive focus" and flow as more like "directed goal focus". For example, if I was working on some interesting problem that required me to research various topics online, I would end up getting distracted by any subproblems that arises and end up going down a rabbit hole. So the idea behind hyper-focus is that mainly with ADHD, it's hard for us to "remember" to keep something in the back of our heads while engaging in any activity thats requires mental effort. That is why a lot of people with ADHD are seen as impulsive as that little thing that many people can keep in the back of their minds is very difficult for me without conscious effort. On the other hand, flow is like when you are in the zone and you have this very clear vision in the back of your mind of the end goal with all the necessary steps needed to achieve that goal outlined already. So in that sense, IMO the intensity of focus would be the same between the two, but the difference lies in the intentionality of it. Not sure if intentionality is the best word, as I believe flow and hyper-focus is unintentional when it occurs but I hope this helps.