Hi, I don't receive any Facebook notifications on my Epix Gen 2. It's the only app that's doesn't show notifications. All settings are on. Any ideas pls...?
More > Settings > Notifications > App Notifications > toggle on Facebook.
How Do I Set Up Which Notifications Display on My Garmin Device?

Is it possible you're not receiving Facebook Messenger notifications? That is a separate app and would also need to be toggled on. Alternatively, you could just toggle on the "All Applications" button, then start blocking those you don't want whenever they appear on your watch.

Personally, I do not want any notifications from Facebook, so I have not tested whether or not there is something wrong, but I've enabled it now to troubleshoot any issues.