It definitely appears much worse for girls, but afaict, depression has risen in boys as well, just by not as much. See graphs here: [1]

So if social medial is harmful in general, I don't view prohibiting it a "punishment" for boys; perhaps like less of a benefit? Regarding your second point, I imagine the data would provide some clues. If the kids that are now teens were always more depressed, I'd imagine that we'd see more pre-teen depression ~3-8 years ago. I haven't looked into it closely.

And I grant that social science statistics are often problematic -- I imagine it'll take a while to really know what's going on.

[1] https://www.afterbabel.com/p/international-mental-illness-pa...