The evidence of social media causing depression and anxiety in youth is mixed and almost all of the affirmative findings are correlational, so I expect to see a variety of takes in this comment thread.

Personally, the strongest positive evidence I've seen comes from the natural experiments tracking when high speed internet & phones were introduced geographically. Rates of teen depression do seem to topple in very close sync with this, as discussed here: https://www.afterbabel.com/p/phone-based-childhood-cause-epi...