The root (top-level) site for your organization can't be deleted. If you're a global or SharePoint admin in Microsoft 365, you can replace the root site with a different site.
And you can create a new communication site that isn't connected to a Microsoft 365 group, then click Replace site of the classic root site in SharePoint admin center, in the URL of the site you want to use box, enter the full or relative URL of the site that you want to become the new root site.
While the old root site is being replaced, it might return a "not found" (HTTP 404) error for few minutes, and you can still access old root site using that archive link:
After replacing the classic root site with a communication site , you can set it as a hub site later.
More detailed information for your reference:
https://learn.microsoft.com/en-us/sharepoint/modern-root-site
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