Managing personal Outlook.com account settings, security, and privacy
When you create a new account and there is no option to choose a hotmail.co.nz domain, then Microsoft is no longer offering that as an option.
If you've got your own domain, then you can consider using Microsoft 365 for Business (or Microsoft 365 Exchange Online) as an alternative so you can use your own domain for sending and receiving emails as well. The web based version is very similar to Outlook.com.