Open the Settings app
Tap Notifications
Select the app you want to silence
Turn off Allow Notifications
To turn off all notifications temporarily, enable Focus mode from Control Center
To mute notifications for a specific time, use Scheduled Summary in Settings > Notifications
To stop notification sounds only, turn off Sounds for the app in its notification settings
To silence messages, open the conversation in Messages and enable Hide Alerts
To stop notification previews, go to Settings > Notifications > Show Previews and choose Never or When Unlocked
To disable badges, turn off Badges for the app in its notification settings