Custom Notifications aka Bell Notifications from the Apex code.

The Messaging.CustomNotification class allows you to create, configure, and send custom notifications using Apex code.

Here is a basic outline of how you can create and send a custom notification from an Apex trigger:

Create a Custom Notification Type: In the Setup, you should create a Custom Notification Type. This defines the type of notification you will be sending from Apex.

Use CustomNotification Class: Once you set up your Custom Notification Type, you can craft your Apex code to create the notification.

Here's an example code snippet:

// Get the Id for our custom notification type

CustomNotificationType notificationType = [SELECT Id, DeveloperName FROM CustomNotificationType WHERE DeveloperName='Lead_Due_Diligence_Completed'];

Messaging.CustomNotification notification = new Messaging.CustomNotification(); 

notification.setTitle('Your Notification Title'); 

notification.setBody('This is the detail of the notification'); 

notification.setNotificationTypeId(notificationType.Id); 

notification.setTargetId('Record ID to which the notification refers, if applicable');

// To send the notification to a single user 

notification.setRecipientIds(new List{'The Recipient User ID'});

// Send the notification try { notification.send(); } 

catch { System.debug('Notification failed: ' + e.getMessage()); }

Please replace 'Your Notification Title,' and 'The Recipient User ID' with the actual values you intend to use.