By default windows user is administrator thanks UAC. By default you install steam as Administrator and there is steam system service. But you can create a sepa

By default windows user is administrator thanks UAC. By default you install steam as Administrator and there is steam system service. But you can create a separate user and leave default one as Administrator. In system policies you can activate a rule where you don't allow users to become Administrator through UAC. And you can install steam as user without the service.