It was a wider blip earlier today, a lot of people saw the same spinner. Usual fix while it sorts itself out: force close the app, toggle airplane mode on and off, then reopen. If it is still stuck, check downdetector before you start reinstalling anything.
Second this. Also make sure notifications are not being throttled by battery saver. – Ella Meyer 3mo ago
0
Mine did the exact same thing for about 40 minutes then came back on its own. If yours is still dead, log in on messenger.com in a browser. If it loads there, it is the app, not your account.