Oppo
Turn Keyboard Sound On or Off auf Oppo
Oppo does not include a global keyboard sound switch inside ColorOS. The company relies on Google's Gboard app as the default keyboard on most models, and that app controls its own key-press sound independently of the system settings.
By default, Gboard ships with the click sound disabled, so a silent keyboard after setup or a reset is normal behavior, not a bug.
To change it, open Settings ➔ Additional settings ➔ Keyboard & input method ➔ Gboard ➔ Preferences, then enable or disable Sound on keypress.
This toggle sits next to vibration feedback options, so check those separately if you only want sound without haptics, or the reverse.
If you use a different keyboard app instead of Gboard, look for the same sound option inside that app's own settings menu, since ColorOS does not enforce it at the system level.