https://www.pbs.org/newshour/politics/read-bidens-full-letter-to-congressional-democrats-declining-to-leave-the-2024-presidential-race

Invoking the 25th involves letter sending. Biden, or the black hats or white hats controlling him, have sent a letter to democrats in congress, and the 25th is being played out quietly now, as to not cause panic in the streets. This has to be done in order to keep people calm.
We may never see the other letters that are being sent, but if there is one letter from either the VP, or the Cabinet, then Joe is done. If they take the 25th to the actual congress, those who support Joe with their vote to keep him around are finished in the eyes of their constituents.
Remember, Trump told us the 25th was going to be in play for Biden. Letters being exchanged are the marker that this is happening right now.
In no other situation would an actual President write a letter to members of their own party to reassure them that they're the only person who can beat their opponent.