In philosophy there's a term "second order desire" which is "wanting to want" something. So, when you want ice cream it's a first order desire, you just want it. But when you want to eat healthily, it's often a desire for wellbeing, long-term goals, etc. Not a sudden urge for carrots.
The challenge for adhd is that second order desires aren't that motivating. When I'm in a sporadic fitness phase (seems to hit for a few weeks every few years) then I really want to exercise (first order desire). I'd rather do exercise than play on my phone or watch TV. But the rest of the time I want to want to do exercise (to be fit) and if I had a magic wand or a pill I could take I'd prefer that to the exercise, because it's not something I genuinely want for itself. But going for a walk somewhere beautiful, or going dancing with friends, are things I genuinely want to do, so are easy to achieve. And they have a byproduct of being some physical exercise.