Sitting still is usually not conducive to focus in the ADHD brain. UNLESS the activity is so entertaining it releases the brain pleasure/focus chemical dopamine (video games anyone).
A common complaint of the digital generation when asked to do something they don’t enjoy is that it isn’t fun or its boring. Actually, many adults have the same complaint.
Who said it has to be entertaining to be worth doing?
You know what else releases dopamine? Movement, exercise, using your body in some way. Sitting around increases boredom because you aren’t generating enough dopamine.
Don’t run for the device to get your fix, get moving. Listen to music while taking a walk. Find entertainment in nature or a museum that requires you to walk.
Engage life for your fix of natures’ focus chemical instead of a device that encourages you to sit still and merely consume.