Hi there,
As it seems that the MDT is not pushing your updates and isn't applying the Local Group Policies, it would be right to start your troubleshooting by analyzing the logs first.
Each MDT script automatically creates log files when running. The names of these log files match the name of the script.
The MDT log file format is designed to be read by CMTrace. Use this tool whenever possible to read the log files, because it makes finding errors much easier.
CMTrace https://learn.microsoft.com/en-us/mem/configmgr/core/support/cmtrace
Then based on your error code we can troubleshoot the issue. For example Error code 9903 means an Unexpected issue installing the updated Windows Update Agent. You can get the error code list from the below link.
Troubleshooting Reference for the Microsoft Deployment Toolkit https://learn.microsoft.com/en-us/troubleshoot/mem/configmgr/troubleshooting-reference
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