Oppo
Change Notification Volume auf Oppo
On Oppo phones running Coloros, notification sounds use a dedicated volume channel that is separate from ringtone, media, and alarm volume. If app alerts or incoming text messages are too loud or too quiet, adjusting the ringtone slider will not fix it, because the system treats notifications as an independent audio stream.
To change it, go to Tap on Settings ➔ Tap on Sound & vibration ➔ Set the Notifications volume. Drag the Notifications slider to the level you want. The change applies immediately to all apps that use the standard notification channel, including messaging apps and system alerts.
When this setting has no effect
If Do Not Disturb is active, notification sounds may stay muted regardless of the slider position, since Do Not Disturb overrides the volume setting for most alerts. Some apps also let you set a custom notification sound or channel volume inside their own settings, which can override the system-wide value for that app only.
If only one app stays silent while others work fine, check that app's individual notification permissions and sound settings rather than repeating the system-wide steps.