For the lock screen, we have two different ways to display changing backgrounds: One is to add your own pictures from the gallery and the other is to use wallpaper services like Samsung Global Goals or the Dynamic Lock Screen.

The Dynamic Lock Screen displays changing wallpapers from a selected category. The categories available are Landscapes, Everyday, Food, Pets and Art. Approximately every two weeks, the wallpapers for the Lock Screen are automatically updated.

Android 10 (One UI 2.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Lock screen
Step 3:  Tap on  Wallpaper services
Step 4:  Tap on  Dynamic Lock screen
Step 5:  Tap on  Apply
  1. Open the Settings
  2. Tap on Lock screen
  3. Tap on Wallpaper services
  4. Tap on Dynamic Lock screen
  5. Tap on Apply

Samsung Instructions