Azure connect, how to correctly set up synchronization so that the correct user principal name is created?

Question

Active Directory

Hi guys. I started to study the issue.
Now there is an AD and I'm trying to synchronize it with Azure AD

. Initially, I registered with [email protected] And after that I already added the main domain mydomain.group.

Now in "Custom Domain Names" there are two
mynamegmailcom.onmicrosoft.com
mydomain.group (set as primary and verified)

But when I try to sync Azure AD connect all users are created with "User Principal Name"

@mynamegmailcom.onmicrosoft.com
And I need with
@ mydomain.group

There are no such settings in azure ad connect itself. I can't find it on the portal.