I have been trying to find information on this - but couldn’t find any real scientific literature. Anecdotally, it’s true for me and my current psychiatrist was the first one to recognise the link and start treating my ADHD instead of the depression and low energy and fatigue that I went to her for. Not there yet. But can confirm that the meds help a lot.

It's not the only cause, but yes.

Could also be hormonal, sickness, stress, lack of quality sleep/nutrition, etc. for men the drop off in testosterone definitely can manifest in feelings of lethargy.

yeah because hyperfocus or losing track of how much energy you are wasting on spurious tasks.