placeholder – working on refining this answer to meet SE standards… (I began by posting links that I thought had the essential info … but actually didn’t…)

Update: WOAH! This is way more complicated than I thought! Even after finding and reading the info at the links below.

Facebook is deceptive. Even after ending ALL Messenger app sessions, I could still log back in in the app without my password and without 2 factor authentication (which I DO have enabled!) I would try to use the app and it would let me right in and a new session would appear. And after killing that session, the above would happen again. I tried killing ALL sessions, and that did the trick. At least this once.

I found info at two facebook.com web pages that I thought p