Facebook and Instagram are easy to diagnose: people post only their wins and their anger, so you end up feeling miserable and/or angry. It's like going to a party where everyone is richer and more beautiful than you, and they are all talking about politics. Same for twitter.
Reddit is more about simple time-wasting and dopamine hits.
YMMV but I honestly felt much better nearly immediately. My life didn’t change in any macro sense - same job, same relationships etc, but baseline mood improved.
Again YMMV, and I’m loathe to say Facebook or Reddit or Twitter or anything is bad or evil or even addictive. I’m not a crusader. But for me going on Facebook for an hour subjectively made me less happy than not going on Facebook.