Not all webcam are compatible with Windows Hello.  Your webcam may not have biometric recognition requirements such as Intel RealSense or 3D camera.  Webcam with infrared sensor should work.  Logitech BRIO is compatible with Windows Hello if you are interested.  
I just installed a Logitech C505e webcam on my new XPS 8950.  The video and sound work fine when testing with the Windows 11 Camera app. I currently use a PIN to log in.  I would like to use Windows Hello Facial Recognition to log into Windows when I boot up.  (I do this on my XPS 15 laptop.)  On the XPS 8950, Settings > Accounts > Sign-in options > Facial recognition, it says "This option is currently unavailable.  We couldn't find a camera compatible with Windows Hello Face."  The Setup button is grayed out. Anyone know if this can be resolved so I can use Hello Face Recognition? Thanks!
XPS 8950, Windows Hello Logitech webcam login not working