Custom email domain: email not available in "From" in icloud+
I followed instructions (Add an email domain you already own to iCloud Mail on iCloud.com - Apple Support) and added a custom email such as xxx@mydomain.com in my iCloud+ custom email domain settings. It shown up in the Custom Domain. I can receive email from any external address. However, I cannot find the email address when I and trying to send a mai. The custom email does not show up in the From dropdown. Only my iCloud email and "Hide My Email" options show up.
I tried to delete the custom email, wait for an hour, and added it back. Tried in from my Mac as well as my iPad. No luck. What am I missing? Appreciate help please!
MacBook Pro 14″, macOS 13.1