This was a very enlightening read. I too spent far too many of my teen years down the tumblr rabbit hole, as did my friendship group at school.
Whilst I never identified with becoming trans, (one of my school friends did and is still trans to this day), I definitely related to the part about tumblr glamourising poor mental health, eating disorders and self harm, and those things did have a significant impact on my teen years and my early 20s.
I really think tumblr, and social media in general, has a lot to answer for, and there needs to be much more safeguarding for young people online