I disagree. Ask any 20-30 year old and I don't think many will say that TikTok, Instagram, etc is "harmful to your health". Maybe a "bit addictive", maybe a few people who say "I have a problem with it". But never "I know this is very harmful for my attention span, my mental health, etc".
Early 20's here, and avoid TikTok, Instagram, etc and know Reddit and the like are all of those things listed - though the worst affected for me personally is attention span.
I usually just like to chime in when people mention stuff like "no one young <does|knows|cares about> $THING", because I've noticed a trend where the fact that there are young people who care is ignored which I think hurts the case more.
Most of my peers don't care however, at least, not as much as I do though I've made some inroads.