Microsoft Defender Locked by Unknown Admin Policies on My Personal PC

“Not Configured” in Local Group Policy does not prove that no other management source has set Defender policy. Microsoft documents several sources with different precedence, and the Policy Manager location you found is associated with MDM configuration. Its presence alone cannot establish whether management is still active or a setting is obsolete.

Use Get-MpPreference to capture effective exclusions and ASR settings, then generate a full gpresult HTML report and an MDM diagnostic report. Keep those reports private. Ask the former institution to check whether this device remains in its Defender or endpoint-management inventory; removing a work account is not evidence that every security-management channel was removed.

DisableLocalAdminMerge explains why a local exclusion can fail to affect the effective configuration. Identify and remove the obsolete assignment through its original management source, then verify the policy. Avoid bulk registry deletion or broad Java exclusions; these observations do not justify reinstalling Windows yet.