Why are my scores lower with Windows 10 build 20H1 (19041.450)?

Microsoft recently released an update to Windows 10’s Microsoft Defender application which makes it impossible to permanently disable the Microsoft Defender Antivirus protection service. This change appears in Windows 10 build 20H1 (19041.450), and is part of KB4052623. As per the Microsoft documentation, this setting is no longer necessary, as Defender will automatically disable itself if third party AntiVirus software is installed on the system.

Customers running BAPCo benchmarks on Windows 10 build 20H1 (19041.450) may notice a negative impact to benchmark scores as a consequence of this update.

BAPCo is also investigating a known issue with Windows 10 build 20H1 (19041.450), in which the PDF results file may incorrectly report the state of Microsoft Defender as disabled.