Turn off the target app's Setting
In the case of Twitter
1.Tap the 'Apps & notification' from the OS settings.
2.Select Twitter.
3.Tap the 'Notifications' .
4.A list of notification channels will be displayed . Set the necessary channels ( such as Direct messages ,Emergency alerts ...).
5.Tap the character part of the 'Direct messages' etc. to be set, and set as follows.
Sound : None
Vibration : OFF
Blink light : OFF
* If These are not displayed , tap the ’Advanced' .
* About channels
Twitter has many channels, but you should usually set the following channels.
Direct messages
Related to you and your Tweets
News
Followers and contacts
Recommendations from Twitter
Tweets from people you follow
It is recommended to operate the channels that seem to be important without muting the sound.
Emergency alerts
Security