iPhone not receiving notifications for Messenger and Outlook

One possibility is that Focus Mode or Do Not Disturb might have been enabled, which silences notifications from all apps unless they’re specifically allowed. You should also check if Background App Refresh is turned on for those apps, as that allows them to fetch new data and send you notifications.

Another thing to consider is whether low power mode has been activated, as it can delay notifications to save battery.

If none of this helps, maybe reinstalling the apps might be worth trying.

I actually just ran into this. I have a Work Focus filter setup, that basically lets all notifications through, but something got out of wack and I had to reset my configurations, now everything is coming through as expected.