This is the answer. Use any fleeting motivation to construct the habit. Do not rely on “feeling like it”. Once you’ve created the habit, it will feel uncomfortable not exercising.
I, and I suspect other ADHD people, don't form those habits.
I've for years read things like "you don't have to remind yourself to brush your teeth because it's a habit. You can make exercising a habit, too."
But for some of us, we do have to remind ourselves to brush our teeth, or eat, or whatever thing the average person does "automatically".
But for some of us, we do have to remind ourselves to brush our teeth, or eat, or whatever thing the average person does "automatically".