Customized email notifications is a feature that is available for Jira Service Desk projects and not for Jira Core and Software.
Allow customizations of Emails in Jira Core and Software.
There are use cases where additional information can be provided on event notifications.
You can use Project Automation to customize notifications (you may want to disable the default Jira notifications that you are going to replace with the custom ones).
You can find the Project Automation voice at the bottom of your project settings. Be careful not to confuse it with the Jira Service Desk Automation voice present in the same menu (in case of Jira Service Desk projects).
For further details on this please see: