Hello Jacky,
When you manually modify EnableLUA to 0, you are changing the local state, but the domain controller holds the "source of truth." Upon reboot, the machine pulls the GPO, sees that the policy is defined as Enabled (value 1), and forcibly overwrites your local edit. This confirms your suspicion that Group Policy is the culprit.
To confirm exactly which policy is reverting your change, you should trace the "Winning GPO." Open an elevated Command Prompt or PowerShell as an administrator and run the command gpresult /h C:\temp\gpreport.html. Open that HTML file in a browser and scroll down to the "Settings" section. You are looking for the path Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options. Under this section, locate the policy named User Account Control: Run all administrators in Admin Approval Mode. This specific policy maps directly to the EnableLUA registry key. If this is set to "Enabled" in the report, it will list the name of the GPO responsible for that setting (e.g., "Default Domain Policy" or a specific "Security Baseline GPO").
As long as that GPO is linked to the Organizational Unit (OU) containing your computer object, any local registry change you make to that key will be futile. The EnableLUA key is critical for security baselines, and disabling it breaks modern Windows Store apps and reduces system security, so it is almost always enforced in enterprise environments. To make the change persistent, you cannot use the Registry Editor locally, you must either move the computer to an OU where this policy is not applied or requesting a modification to the upstream Group Policy Object itself. If you are the administrator, you should modify the GPO directly; if you are not, you are fighting a losing battle against domain enforcement.
I hope you've found something useful here. Should you have more questions, feel free to leave a message. If my answer helps you get more insight into the issue, it's appreciated to accept the answer. Have a nice day!
VP