The preset theme on the OnePlus smartphone can also be customized.
Depending on the wishes and needs of the user, we can choose between the following three options:

Android 10 | OxygenOS 10.0
Step 1:  Open the  Settings
Step 2:  Tap on  Customization
Step 3:  Tap on  Preset Theme
Step 4:  Choose a  theme
Step 5:  Confirm with  Apply
  1. Open the Settings
  2. Tap on Customization
  3. Tap on Preset Theme
  4. Choose a theme
  5. Confirm with Apply

OnePlus Instructions