Description
Use this filter to disable admin and user notification emails.
Usage
add_filter( 'gform_disable_notification', 'your_function_name', 10, 4 );
You can also specify this per form by adding the form id after the hook name.
add_filter( 'gform_disable_notification_6', 'your_function_name', 10, 4 );
Parameters
- $is_disabled bool
Variable to be filtered. Set it to true to disable notifications 
-  $notification array Current Notification array 
-  $form Form Object Current form. 
-  $entry Entry Object Current Entry array 
-  $data array Array of data which can be used in the notifications via the generic {object:property} merge tag. Defaults to empty array. Since: 2.3.6.6. 
Examples
Disable ALL Notifications
This example disables admin and user notifications for all forms
add_filter( 'gform_disable_notification', '__return_true' );
Disable a notification based on a field
This example shows you how to disable a notification conditionally based on a field of the entry. This can help you in situations where conditional logic can’t be used (e.g. To send a notification only if an upload field was not used).
add_filter( 'gform_disable_notification', 'disable_notification_by_field', 10, 4 );
function disable_notification_by_field( $is_disabled, $notification, $form, $entry ) {
	$field_to_check = rgar( $entry, '1' ); // Replace 1 by your field id number
	// Replace User Notification by your notification name.
	if ( $notification['name'] == 'User Notification' && ! empty( $field_to_check ) ) { // Disable notification only if $filed_to_check is not empty.
		return true;
	}
	return $is_disabled;
}
Update from gform_disable_user_notification
This example shows you how to update your code from the deprecated gform_disable_user_notification hook
add_filter( 'gform_disable_notification', 'disable_notification', 10, 4 );
function disable_notification( $is_disabled, $notification, $form, $entry ) {
    //There is no concept of user notifications anymore, so we will need to disable notifications based on other criteria such as name
    if ( $notification['name'] == 'User Notification' ) {
        return true;
    }
    return $is_disabled;
}
Update from gform_disable_admin_notification
This example shows you how to update your code from the deprecated gform_disable_admin_notification hook
add_filter( 'gform_disable_notification', 'disable_notification', 10, 4 );
function disable_notification( $is_disabled, $notification, $form, $entry ) {
    //There is no concept of admin notifications anymore, so we will need to disable notifications based on other criteria such as name
    if ( $notification['name'] == 'Admin Notification' ) {
        return true;
    }
    return $is_disabled;
}
Disable based on payment/subscription event
This example shows how a notification assigned to a payment or subscription event could be disabled based on the event properties.
add_filter( 'gform_disable_notification', function( $is_disabled, $notification, $form, $entry, $data ) {
	if ( isset( $data['payment_action'] ) && empty( $data['payment_action']['amount'] ) ) {
		$is_disabled = true;
	}
	return $is_disabled;
}, 10, 5 );
Placement
This code can be used in the functions.php file of the active theme, a custom functions plugin, a custom add-on, or with a code snippets plugin.
See also the PHP section in this article: Where Do I Put This Code?
Source Code
This filter is located in GFAPI::send_notifications() in includes/api.php