In addition to the camera shortcut (default), the camera can also be started from the lock screen by pressing the function button. To do this, the function (Quick Launch Camera) button must be pressed twice. By default, this function is enabled. If not, it can be activated as shown in this manual.

Android 10 (One UI 2.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Advanced features
Step 3:  Tap on  Side key
Step 4:  Tap on  Quick launch camera
  1. Open the Settings
  2. Tap on Advanced features
  3. Tap on Side key
  4. Tap on Quick launch camera

Samsung Instructions