ADHD is a difference in how the brain functions and is constructed.

It is physiological.

I don't think any evidence exists that you can cause anyone to become neurodivergent except by traumatic brain injury

TikTok does not "make" people ADHD. They might struggle to let themselves be bored and may be addicted to quick fixes of dopamine, but that is not what ADHD is. ADHD is not an addiction to dopamine hits. ADHD is not an inability to be bored.

TikTok for example will not give you the kinds of tics and lack of proprioception that is common in neurodivergent people. Being addicted to Tiktok will never give you that absurd experience where your brain "hitches" while doing a task and you rapidly oscillate between progressing towards one task vs another. Being habituated to check your phone at every down moment does not cause you to be unable to ignore sensory input because your actual sensory processing machinery in your brain is not functioning normally. Getting addicted to tiktok does not give you a child's handwriting despite decades of practice. If you do not already have significant stimming and jitter symptoms, Tiktok will not make you develop them.

You cannot learn to be ADHD.