How should you schedule an email to send in Mail on iPhone?
Tap Settings > Mail > Schedule and configure the send date and time.
Touch and hold the mail body and configure the send date and time.
Touch and hold the send button and set the send date and time.
Tap the calendar icon in the mail menu bar and configure the send date and time.
It's right
https://support.apple.com/en-gb/guide/iphone/iph742b6abb1/ios