I too have run into this. Recent 27.0.1 update does not address the issue.

Updated to Beta 8 and SSO still did not show up. I got it to appear by backing out of the first user account creation step. However once SSO initiated I got this error: The single sign on extension could not validate the domain Since this same profile works as expected with a logged in local user account, I suspect this error message is in error.

Interesting. I haven't been able to get the SSO to prompt during setup at all. Entra asks after setup is done but nothing during enrollment/setup. Trying with Beta 8 now.