The Gboard keyboard on the Oppo smartphone can be changed to 7 different sizes, with the choice of Very Low, Small, Rather Small, Normal, Rather Large, Large, Very High.

Android 10 (ColorOS 7.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Additional settings
Step 3:  Tap on  Keyboard & input method
Step 4:  Tap on  Gboard
Step 5:  Tap on  Preferences
Step 6:  Tap on  Keyboard height
Step 7:  Choose desired  Keyboard height
  1. Open the Settings
  2. Tap on Additional settings
  3. Tap on Keyboard & input method
  4. Tap on Gboard
  5. Tap on Preferences
  6. Tap on Keyboard height
  7. Choose desired Keyboard height

Oppo Instructions