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Thank you for the detailed information about your environment and the troubleshooting you have already performed.
Based on the information provided, this behavior is expected on Windows 11 Pro.
The Force a specific default lock screen and logon image Group Policy is not supported for configuring the lock screen on Windows 11 Pro. The following GPO support for the lock screen:
- Windows 11 Pro / Pro Education: GPO is not supported.
- Windows 11 Enterprise / Education: GPO is supported.
- Windows 11 IoT Enterprise: GPO is supported.
Therefore, seeing the policy in GPResult or RSOP does not mean that this particular setting will be enforced on Windows 11 Pro. Please notes that Force a specific default lock screen and logon image applies only to Enterprise, Education, and Server SKUs.
This also explains why your Desktop Wallpaper GPO works successfully. The desktop wallpaper GPO support for Pro / Pro Education, Enterprise / Education, and IoT Enterprise, while the lock-screen GPO has different edition requirements.
For Windows 11 Pro devices, you may want to consider management through Microsoft Intune/CSP instead. The Personalization > Lock Screen Image Url setting and the ./Vendor/MSFT/Personalization/LockScreenImageUrl CSP for configuring the lock screen.
However, please review the applicable requirements before using this method. The Personalization CSP is supported on Enterprise and Education and works on Windows Professional when SetEduPolicies in SharedPC CSP is set or when the device is configured in Shared PC mode with the BootToCloudPCEnhanced policy.
If Active Directory Group Policy is the required management method, the supported policy on Enterprise or Education is:
Computer Configuration > Administrative Templates > Control Panel > Personalization > Force a specific default lock screen and logon image
For supported editions, the policy accepts a fully qualified local path or UNC path for the image.
Therefore, based on your current configuration, the fact that the lock screen remains unchanged on Windows 11 Pro is consistent with the documented edition limitation rather than indicating that the GPO itself has failed to apply.
References:
Configure the Desktop and Lock Screen Backgrounds in Windows | Microsoft Learn
Personalization CSP | Microsoft Learn
Customize the Lock Screen in Windows | Microsoft Support
ADMX_ControlPanelDisplay Policy CSP | Microsoft Learn
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