Fake news has been harming democracy since democracy was invented. Remember those indian scalpings? Mostly made up by Benjamin Franklin to rally support for colonial gov.
If anything social media is a benefit to democracy vs. legacy media because it dilutes the power of any one voice, it's very hard to control all social media whereas a couple conglomerates now own nearly all of legacy media.
Looked at another way, if democracy cannot withstand social media and made up stories then it's not a stable system of government. Stories of the end of history are greatly exaggerated, historically democracy is far less successful than autocracy, perhaps due to this issue.
a hallmark of fascism and dictatorships is the capture of media, and the censorship of it.
i find it hard to accept that the solution to your problem here is that democracy must fall because of propaganda, when the very same propaganda is what leads to dictatorship.
Without a way to create objective dialogue, what is any system of government other than the picture it paints. Facts, and nothing else, is the only way to maintain a democracy.
Once you permit subjectivity, conjecture, and propaganda, like, say... when right wing billionaires buy create fox news, buy cnn, john oliver, colbert, every local news network (sinclar), washington post, tik tok, twitter, etc etc etc etc etc........ democracy is no longer possible.
The stability of autocracy is greatly exaggerated. It often can't even withstand the leader dying. Government stability is the great feature of democracy. I'm not quite as confident as I used to be, but I'm still pretty confident that my country will have a new leader in 2029 and that there will not be a violent civil war accompanying the transition.