SharePoint Online Site Swap
Wondered how to get the old Classic Site and turn it into the new Modern Communication Site?
Microsoft started rolling out to tenants with less than 10k users this past week. All others will be taken care of by Halloween. Admins will be able to swap the SharePoint root site with another site using a new PowerShell cmdlet Invoke-SPOSiteSwap. The root site will be archived automatically. You must use the SharePoint Admin PowerShell version 16.0.8812.1200 or later.
Here is an example of the code: Invoke-SPOSiteSwap -SourceUrl https://tenantname.sharepoint.com/sites/CommunicationSite -TargetUrl https://tenantname.sharepoint.com -ArchiveUrl https://tenantname.sharepoint.com/sites/Archive
Remember the source or target sites cannot be "associated" with an Office 365 Group or a Hub Site. If the site is a Hub then remove the association then add it back when you are done.