You can send group emails directly from the Mail app. To do so, go to the Mail app, compose an email, and in the "to/cc/bcc" field, type in the first few letters of your group, and the Mail app will prompt you to select your group. Please note that this will only work with the Mail app, and NOT the Gmail app.
You can send group messages directly from the Messages app with iOS 13 or later. To do so, go to the Messages app, compose a message, and in the "to" field, type in the first few letters of your group, and the Messages app will prompt you to select your group.
You can also send group emails and messages using A2Z Contacts, a contact management app: