In a Multi-Geo tenant, you can store your user's data in a different geographic location than your tenant.
If you connect to a Multi-Geo tenant, the URLs will look like standard SharePoint URLs in ShareGate Desktop. For example:
When you access that OneDrive in your Multi-Geo tenant, the URL is modified to fit the OneDrive's location. For example, if the OneDrive is in the United-States, .us is added to your domain:
Because it is technically a different domain, the connection fails when you try to access that OneDrive directly without the location (.us) added to the domain in the URL.
When migrating a site or OneDrive for Business in a Multi-Geo tenant, you have to connect with the URL that specifies the location in the domain.