The background image of the lock screen can be set independently of the home screen.
Here, in addition to the constantly changing daily backgrounds, we can also set a pre-installed image or our own photos to further customize the OnePlus smartphone to the user's needs.

Android 10 | OxygenOS 10.0
Step 1:  Open the  Settings
Step 2:  Tap on  Customization
Step 3:  Tap on  Wallpapers
Step 4:  Select the  lock screen
Step 5:  Tap on  My photos  or swipe  left/right  to browse the  wallpapers
Step 6:  Select a  wallpaper
Step 7:  Tap on  Save
  1. Open the Settings
  2. Tap on Customization
  3. Tap on Wallpapers
  4. Select the lock screen
  5. Tap on My photos or swipe left/right to browse the wallpapers
  6. Select a wallpaper
  7. Tap on Save

OnePlus Instructions