Don't underestimate TikTok. You can find all sorts of weird fad mental illness there. For a while tourette syndrome was all the rage and the platform was filled with kids faking tics. There are fake epileptics faking seizures too. OCD is another common "cool" self-diagnosis and there are online quizzes to tell you how OCD, or ADHD or bipolar you are. It wouldn't surprise me at all if schizoid or schizotypal caught on.
I think some people are looking for the self-validation that can come with a diagnoses, an explanation for why they are the way the are, feel the way they do, or why they struggle with certain things. Others are just looking for views, attention, or a community to belong to.
While it can be fairly harmless the ability for mass sociogenic illness to spread via social media is interesting and a bit frightening.