From https://android.stackexchange.com/questions/179664/how-do-i-…
I used to be able to receive push notifications for all postings to a specific group. that option no longer appears anymore. please see https://photos.app.goo.gl/CsDyZ1um9dHAqs883 if the image link doesn't work
Launch the Facebook app on your iPhone or iPad.
Tap the hamburger menu in the bottom right corner of the app (looks like three stacked lines).
Scroll down and tap on Settings.
Tap Account Settings.
Tap Notifications.
Tap Group posts.
Tap the name of the group for which you want to adjust notifications.
Tap On under both Notifications categories to disable notifications.
Hope this will help…