Depending on the smartphone model, notifications are indicated by the notification LED on the front of the Samsung device. Alternatively or additionally, the receipt of a new notification can also be indicated by the flashing of the camera flash. Flash notification is deactivated by default and can be found deep in the settings.

Android 10 (One UI 2.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Accessibility
Step 3:  Tap on  Advanced settings
Step 4:  Tap on  Flash notification
Step 5:  Enable or disable  Camera flash
  1. Open the Settings
  2. Tap on Accessibility
  3. Tap on Advanced settings
  4. Tap on Flash notification
  5. Enable or disable Camera flash

Samsung Instructions