I just saw this message (image above) on my Messenger desktop app and it appears that META a.k.a. Facebook wants to bring users back to Facebook.com, since users will be redirected back to Facebook.com after Dec. 15. The Messenger app shutdown affects both the Windows and Mac apps of Messenger.
And if you are worried about your chat history, Meta encourages users to “enabled secure storage in Messenger should turn on secure storage and setup a PIN from their desktop app.” You can visit this Support page for the FAQ’s and additional information on Messenger app on desktop.
