https://support.apple.com/en-us/HT213158
If you subscribe to iCloud+, you can purchase your own domain. Then you can send and receive email from a personalized email address with iCloud Mail…
Purchase a domain on your iPhone with iOS 16 or later
Open the Settings app.
Tap your name.
Tap iCloud, then select iCloud Mail.
Select Custom Email Domain, then tap Continue.
Select Buy a Domain.
In the text field, enter the domain name that you want to purchase.
Tap Search. If the domain or similar domains are available, pricing options are listed.
Select a domain, then follow the onscreen steps to complete your purchase. ..
