I want to disable Messenger notifications from vibrating on my iPhone iOS 12, but keep them silent. How to do that? There doesn't seem to be an option for it anywhere.
To disable vibration in Facebook Messenger on iOS 12, open the app the tap your profile icon in the upper left hand corner.
This will open your "Me" page. You'll see the fourth option, notifications. Tapping on it will open the notifications page. You can then select the option "Notifications in Messenger."
That will then open a page where you can toggle sound and vibration for notifications.