It's just not supported. Microsoft Defender Antivirus will lack a user interface when used with Windows Server 2012 R2 with the new unified solution stack preview.

Microsoft on Monday announced that its Microsoft Defender for Endpoint security solution now supports older Windows Server products, namely Windows Server 2012 R2 and Windows Server 2016.

“In line with Microsoft's longstanding and deep commitment to security and our ongoing engagement with third party extensions to our products, we are pleased to see ThreatTrack Security build VIPRE ...