These steps, experts say, could prod more people to abandon the scourge of hoaxes and lies. Last month, millions of Americans watched as President Biden took the oath of office and, in a high-minded Inaugural Address, called for a new era of American unity. But plenty of other Americans weren’t paying attention to Mr. Biden’s speech. They were too busy watching YouTube videos alleging that the inauguration was a prerecorded hoax that had been filmed on a Hollywood soundstage. Or they were melting down in QAnon group chats, trying to figure out why former President Donald J. Trump wasn’t interrupting...