Windows Hello Face Unlock No Longer Works in the Dark and Microsoft Says It's Not a Bug (windowscentral.com)
Windows Hello earlier relied solely on infrared sensors to create 3D facial scans, allowing the feature to work in complete darkness similar to iPhone's Face ID. Microsoft pushed the dual-camera requirement to address a spoofing vulnerability in the biometric system.
[1] https://www.windowscentral.com/software-apps/windows-11/windows-hello-face-unlock-no-longer-works-in-the-dark-and-microsoft-says-its-not-a-bug