Here are updated instructions that have already helped other users:
On computer (Windows/macOS):
Open Discord → click the gear icon at the bottom (User Settings).
Go to the Notifications section.
Here you can:
Enable or disable all sound notifications;
Configure notifications for messages, mentions, and calls;
Disable notifications when you are in streaming mode.
Additionally:
Right-click on a server → select Notification Settings → adjust notifications for that specific server.
On phone (Android/iOS):
Open the Discord app → tap your avatar → choose Notifications.
Here you can:
Manage push notifications;
Enable/disable vibration;
Adjust how notifications behave in silent mode.
Additionally:
In your phone’s system settings (outside the app), check whether Discord notifications are allowed.