Currently there is no way to clone a variant through the page manager edit page.
Add an operation for the variant that would allow the "clone" of the variant for use.
I will attach a patch shortly. It will need testing though.
When visiting `admin/structure/page_manager/manage/{page}` each variant has a new operation under the dropdown called clone.
Needs review
4.0
User interface
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
For RC2, accessing the "general" tab of a variant causes this error with the patch:
Symfony\Component\Routing\Exception\MissingMandatoryParametersException: Some mandatory parameters are missing ("page_variant") to generate a URL for route "entity.page_variant.clone_form". in Drupal\Core\Routing\UrlGenerator->doGenerate() (line 181 of core/lib/Drupal/Core/Routing/UrlGenerator.php).