ADHD doesn't even really mean short attention spans, it's more of the inability to willingly direct attention. It's the same way people incorrectly use "OCD" to mean liking things clean and/or orderly.

Both of these are the product of needing constant stimulation. I understand your point that hyper-focus is also part of ADD/ADHD, and I certainly am not going to make claims about how your brain is changing structurally without evidence behind it.

So this is mere conjecture for a mechanism:

What these apps (with short format video being the worst) do is train your brain to expect a constant stream of dopamine hits. Novelty (presumably even trash novelty like TikTok) triggers dopamine, your brain becomes dependent on that steady stream of dopamine fix, and your body starts craving it once you remove that pattern of behavior.

This is very similar to ADHD, which is also strongly connected to problems with how dopamine is regulated. It's not as simple as just not enough dopamine or poor uptake or whatever, but it's reasonably clear that it plays a role.

So both cases are a result of poor dopamine regulation causing a need for stimulation that has a negative impact on ability to function from day to day. They're probably at minimum relatively similar.