Ehhhhhh, I think it's a little of column A and a little of column B.

I think the biggest tik tok contributor is people now hear about ADHD and decide because they get bored in schoo sometimes they must have it etc. (As someone who struggles not to chew through their own gums as a form of fidgeting, I find this really irritating.) But let's put that aside because I don't think that's what you're asking about. I'll also ignore the fact that more people are walking into therapists having read all the symptoms and knowing essentially what to say to receive a "diagnosis."

To the actual question, I do think TikTok/smartphones/internet are definitely rewiring our brains in ways that mirror a lot of symptoms of ADD/ADHD. There's a depressingly good book about it called the Shallows but the basic thesis is that the financial incentives of the internet are geared to keep you clicking and moving through things (so you see more new ads) which habituated people to very short term impulses/reward structures. In other words, impulse control and trouble focusing long term.