Final answer:
To ensure Windows Defender's real-time protection remains on, the Group Policy's "Turn off real-time protection" setting should be set to Disabled.
Step-by-step explanation:
To ensure that Windows Defender's real-time protection is always on and cannot be overridden by other users, including local administrators, the "Turn off real-time protection" setting in the Group Policy Management Editor should be set to Disabled. When this policy is Disabled, it means that real-time protection cannot be turned off through the policy setting.
If you were to select Not Configured, real-time protection could still potentially be turned off by users through other means. Choosing Enabled would mean that the policy actively turns off real-time protection, which is not the desired outcome. Therefore, the correct choice to keep real-time protection always on is to set the policy to Disabled.