RG26 (West Europe) contains temporary resources including SQLDB01, which is backed up to RGV1. Deleting RG26 from the portal fails. What should you do first to allow deletion of RG26?

The most immediate action to enable the deletion of RG26 is to stop the backup of SQLDB01. Azure Resource Groups cannot be deleted if they contain resources that are still actively being backed up, as the backup process creates dependencies that prevent deletion. Stopping the backup releases this dependency. Deleting VM1 or stopping VM1 (assuming it's in RG26) might be necessary eventually, but the backup dependency is a common blocker for resource group deletion when databases are involved. Deleting sa001 (a storage account, presumably) is unlikely to be the primary blocker for a resource group deletion unless it's explicitly configured as a backup target with active processes preventing deletion.