After introducing a capability to send custom notification to a group of devices (see https://t.co/m2rBPUjV0S), Intune has been updated to allow you to send such custom notification to a specific device.
The principles are the same as for sending to a group of devices.
To send a custom notification to a specific device, logon to your Azure portal (https://portal.azure.com) or Intune portal (https://devicemanagement.microsoft.com) and go to the Intune\Devices (Azure portal) or the Devices (Device Management portal) section
Then access the All Devices blade and select the device you want to send the notification
Finally open the …More menu and select Send Custom Notification
And define the notification title and content
That’s it.