A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
MS couldn't automatically create a Communication site for one user account.
You could follow these steps to solve your issue:
1.View the details of this alias group
Go to the Microsoft 365 admin center page, and then click Active groups option under the Groups section, select this alias group to view the detail pane.

2.On the detail pane, If you want to use this alias, you could choose delete or edit this alias group.

3.Of course, you could entry another group name when creating a SharePoint Site.
You could refer to this article Unable to create the Office 365 group as there is already a group with the same alias.
Thanks,
Echo Du
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