Open the Facebook app
Tap the Menu icon
Go to Settings & privacy
Tap Settings
Scroll to Preferences
Tap Media
Turn off Sounds in the app
On iPhone, also turn off the Ring/Silent switch if needed
On Android, also lower or mute media volume if needed
To stop notification sounds, go to Notifications in Settings
Turn off notification sounds for Facebook
On desktop, click your profile picture
Go to Settings & privacy
Open Settings
Go to Notifications
Turn off sound notifications if available