Getting started wizard in Azure Virtual Desktop

You note that "AD Domain join UPN cannot include reserved words" as listed in the linked page. Are you referring to the account used to join the domain, or the domain itself? Specifically, when creating AADDS, can I use reservedword.mydomain.com for my domain? Does it matter if the the Azure AD user account being used to join the domain is useraccount@mydomain.com instead of useraccount@reservedword.mydomain.com, with reservedword.mydomain.com being specified as the domain to join when deploying a session host? (My situation is that I used a reserved word as part of my AADDS subdomain, and I'm wondering if I will need to start from scratch or perhaps try to rename it.)