Dewey Digital's latest report on the exodus from X is a great read:

Our latest update for Q3 2023 — now renamed the “X/Twitter Migration Report” — finds that Elon Musk’s rebranding of Twitter to “X,” as well as the ongoing struggles and controversies surrounding the platform, have had negative consequences for X/Twitter, which continues to experience a steady decline in usage and advertising revenue. We also found that Threads, after its initial burst of growth and subsequent decline, has emerged as a steady competitor to the X/Twitter platform. And the trends we’ve been identifying — particularly the continued emergence of open social protocols — are ongoing.