Some reports estimate that around 1M people have left #twitter in the last weeks https://www.technologyreview.com/2022/11/03/1062752/twitter-may-have-lost-more-than-a-million-users-since-elon-musk-took-over/. At the same time #mastodon has grown in 860k users since Nov 4th. Here is the plot of the number of users in the #mastodon instances at http://instances.social in the last months.