Once TalkBack is activated on the Oppo-Smartphone, it can only be deactivated again with a slightly different control. A single tap selects the corresponding function/App (green border). A double tap then executes the action.

Android 10 | ColorOS 7.0
Step 1:  Tap on  Settings
Step 2:  Double-Tap on  Settings
Step 3:  Tap on  Additional settings
Step 4:  Double-Tap on  Additional settings
Step 5:  Tap on  Accessibility
Step 6:  Double-Tap on  Accessibility
Step 7:  Tap on  TalkBack
Step 8:  Double-Tap on  TalkBack
Step 9:  Tap on  TalkBack
Step 10:  Double-Tap on  TalkBack
Step 11:  Tap on  Turn off
Step 12:  Double-Tap on  Turn off
  1. Tap on Settings
  2. Double-Tap on Settings
  3. Tap on Additional settings
  4. Double-Tap on Additional settings
  5. Tap on Accessibility
  6. Double-Tap on Accessibility
  7. Tap on TalkBack
  8. Double-Tap on TalkBack
  9. Tap on TalkBack
  10. Double-Tap on TalkBack
  11. Tap on Turn off
  12. Double-Tap on Turn off

Oppo Instructions