You can copy site collections using the Copy structure and content option in ShareGate Migrate.
Index
Prerequisites
You have site collection admin permissions on your source site collection(s).
You have site collection admin permissions on your destination site collections if you want to merge your source site collection into an existing site collection.
You have term store admin permissions on your source and destination if you have managed metadata (Terms, Term sets, Term set groups) in your migration scope.
Note: Site collection admin permissions are required even if you have higher admin privileges like SharePoint admin or global admin permissions. For more information, see Microsoft administrative permissions.
How-to
Tip: To migrate multiple site collections, you can connect to your central admin or admin center in steps (3) and (7). You will need SharePoint admin, farm admin, or global admin permissions.
Select Copy from the menu.
Select Copy structure and content.
Click Connect.
Select your source.
Click Next.
Click Connect.
Select your destination.
Click Next.
Select Sites from the list of Site objects.
Select the site collection(s) you want to copy from the source.
Tip: You can uncheck List content under Configuration in your copy options to migrate your sites' structure without documents and list items.
Drag and drop it into the site level at the destination, or click Start copy on the bottom-right corner.
When the action is completed, the migration report will show any successes, warnings, or errors. See Migration Report for more details.