The hidden or private photos or videos in the Oppo smartphone's gallery can be restored at any time.

To do so, open the gallery and hold the status bar or the tabs bar (Photos - Albums - Explore) in the upper area. After a short confirmation with the specified unlock method via PIN, password, pattern or fingerprint or face recognition, the hidden files are displayed.

Android 11 | ColorOS 11.0
Step 1: Tap on  Photos
Step 2: Tap and hold the  Tab bar  and enter the  Unlock method
  1. Tap on Photos
  2. Tap and hold the Tab bar and enter the Unlock method

Oppo Instructions