Photos or videos deleted on Oppo smartphone will be moved to the Trash for 30 days, and since there is no way to disable the Gallery Trash, the Trash must be emptied manually if you want to remove the photos from the device immediately.

Android 10 | ColorOS 7.0
Step 1:  Open the  Photos -App
Step 2:  Tap on  Albums
Step 3:  Tap on  Recently deleted
Step 4:  Open the  Menu
Step 5:  Tap on  Select
Step 6:  Tap on  Delete All
Step 7:  Confirm with  Delete X Items
  1. Open the Photos-App
  2. Tap on Albums
  3. Tap on Recently deleted
  4. Open the Menu
  5. Tap on Select
  6. Tap on Delete All
  7. Confirm with Delete X Items

Oppo Instructions