Windows Defender Turned Off By Group Policy (Resolved)
Using Registry Editor Step 1. Then you open the Registry Editor by pressing Windows key + R then type regedit and tap Enter. Step 2. Go to: HKey_Local_Machine\Software\Policies\Microsoft\Windows Defender Step 3. Delete DisableAntiSpyware registry key Step 4. Restart your system to take effect.
Enable Windows Defender via Group Policy Step 1. Open Local Group Policy Editor by pressing Windows Key + R then type gpedit.msc and click OK. Step 2. Go to Computer Configuration > Administrative Templates > Windows Components > Windows Defender
Step 3. In order to turn on Windows Defender, you select Disabled. Click OK to save the settings. Step 4. Reboot your system.
You can also see this video below to learn more how to fix Windows Defender "This app is turned off by group Policy" problem in Windows 10