Google says the Pixel 8 series feature a Face Unlock that is very secure and is Class 3, which is the highest Android biometric class standard.
The Mountain View giant says the Pixel 8 and Pixel 8 Pro feature a Face Unlock that is very secure and is Class 3, which is the highest Android biometric class standard. What this tech means is that it is very unlikely that someone else will be able to unlock the phone through the face. However, the Reddit user claims otherwise. There are chances that Pixel 8's Face Unlock system was fooled by the sibling's resemblance.
There are chances that this could be a bug in the system that might be exploited by someone who looks similar to the owner of the phone. Google hasn't responded to the issue and at this point, it is not clear whether this is an actual vulnerability or as said just. a bug that can be fixed through a software update.