1) It was a 4 week experiment. This may show that the participants had become too reliant on Facebook for news. It seems likely that people will adapt after qutting Facebook entirely.
2) How likely is activism to come from people who are only connected to the outside world via Facebook?
3) Reduced "factual news knowledge" is not the same as "didn't know about the Roe verdict". I was somehow aware of the verdict without being on Facebook. It's hard to tell from just the abstract, but we don't know how they define "factual news knowledge". In my opinion, most so-called "news" is just trivia and unimportant. Politician A said X, politician B said not-X, blah blah, ad nauseam. IMO it's actually better to take a step back from the daily trivia and look at the broad historical perspective. Better to read a book than a headline. A person can become "too informed" about things that don't matter, missing the forest for the trees.