9to5 Mac did some sleuthing in the latest Big Sur beta and found references to the TrueDepth camera system currently found on some iPhones and iPads. Specifically, there are references to “PearlCamera”, which was Apple’s internal code name for the TrueDepth camera.
It makes perfect sense that they would add Face ID to Apple silicon Macs. They have already built it into very similar chips currently shipping on iPad and iPhone, and people would love to have Face ID on their Macs, just like everything else Apple makes. Indeed, you could argue it will be more useful on a Mac since I rarely am sitting at my Mac wearing a face mask. All that said, I would be shocked if Face ID shows up any time before Apple starts shipping Apple silicon Macs.