I have an Azure Cosmos DB and I need to delete all the resources from this subscription. Is there any way to take a backup offline from the portal?
You can use Data Migration Tool suggested on Automatic online backup and restore with Azure Cosmos DB article to do the same.
There is no way to take a backup and import to Azure CosmosDB.
The recommendation is to open a support ticket (e.g. via Azure Portal) or call Azure Support to streamline the backup/restore strategy and to request Azure to restore the latest backup in case of a disaster event. In addition, you can contact the Azure CosmosDB team by sending an email to [email protected].