The camera flash on the back of the OnePlus smartphone also serves as a flashlight, which can be enabled or disabled at any time via the quick settings in the status bar, for example to illuminate dark environments or to provide a little more light in emergencies.

Note: Depending on the arrangement of the quick settings, the flashlight is already accessible via the first six accesses or app icons

Android 10 | OxygenOS 10.0
Flashlight -  Swipe with  two fingers  to open the quick settings
Flashlight -  Enable or disable  Flashlight
  1. Swipe with two fingers to open the quick settings
  2. Enable or disable Flashlight

OnePlus Instructions