Oppo calls it "Eye comfort", it is better known under night mode. the blue light filter is easy on the eyes in dark environments. blue light can be filtered out. the intensity can be adjusted. in addition to manual activation/deactivation, a schedule can also be configured.

Android 10 (ColorOS 7.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Display & brightness
Step 3:  Enable or Disable  Eye comfort
  1. Open the Settings
  2. Tap on Display & brightness
  3. Enable or Disable Eye comfort

Oppo Instructions