With the camera flash, you can take photos even in dark rooms, and in addition to the automatic mode, we can also permanently switch on the flash of the Samsung device (when taking a photo).

Note: The flash is rarely used, especially on mid-range and high-end smartphones. We recommend using the flash only in dark rooms for a natural photo.

Android 10 (One UI 2.0)
Step 1:  Open the  Camera -App
Step 2:  Tap on  Flash
Step 3:  Choose between  Off,   Auto  and  On
  1. Open the Camera-App
  2. Tap on Flash
  3. Choose between Off, Auto and On

Samsung Instructions