Depending on the model, the Oppo smartphones offer us different video resolutions: if HD and FullHD videos are already standard, some models can also record 4K or even 8K videos.

Android 10 | ColorOS 7.0
Step 1:  Open the  Camera -App
Step 2:  Open the  Menu
Step 3:  Tap on  Settings
Step 4:  Tap on  Video Resolution
Step 5:  Choose desired  Resolution
  1. Open the Camera-App
  2. Open the Menu
  3. Tap on Settings
  4. Tap on Video Resolution
  5. Choose desired Resolution

Oppo Instructions