Has anyone tried to create new environment in Azure DevOps pipeline using PowerApps Build Tools. If you have and been successful, can you tell me what service connection did you use to populate 'PowerApps Admin Credentials'? If you used 'Generic', what did you enter for 'Server URL' field?
You'll need to create a Generic service connection as you already selected and then enter the URL (e.g. envname.crm.dynamics.com) and credentials of any D365/CDS environment you already have under that tenancy.