EDIT: See e.g. https://www.nationalacademies.org/read/27396/chapter/6#93, and if you think this is what constitutes "clear evidence", well, you have some very questionable epistemological standards.
EDIT2: Also, limit yourself to proper longitudinal studies and then look at the actual effect sizes reported. You will find, yes, there is broad evidence that social media is likely slightly more harmful to adolescents than beneficial / not harmful, but the actual effect size is so tiny broad interventions are unlikely to have practical consequences. I.e. the most plausible explanation is that the vast majority people are not meaningfully affected, and small subgroups benefit and/or are negatively affected.
It is the usual pseudoscientific / social science attempts to launder "statistical significance" (which you get trivially with enough samples) into practical significance, in order to justify sweeping societal changes.