The Messenger app can be configured to reduce its default notification behaviour.
By default on Android, Messenger enables “Chat Heads”, which creates floating buttons that can be annoying to deal with. These can be disabled, along with other notifications by selecting your account settings:
“Chat Heads” and other Notification settings can then be changed:
Sometimes there may be a lot of activity on the Messenger Groups that you can’t participate in, e.g. you’re at work. To temporarily mute notifications, select the “info” button on the Group page:
Select the “Notifications” settings:
Then select to “Mute Notifications”:
And finally select the duration to mute: