Historically, installing Symantec Endpoint Protection (SEP) disabled Windows Defender on Microsoft Windows operating systems.
Recent Windows 10 builds may show Windows Defender as enabled regardless of SEP being installed.
Recent Windows 10 builds introduced new components of Windows Defender that prevent SEP from disabling it.
Example of such Windows Defender component is Limited Periodic Scanning. Enabling that option will keep Windows Defender on and in tandem with SEP.
No action is required as this is expected behavior.
For more information please contact Microsoft.