The 'shipping' kernel 5.10.63+ does reboot. When the 'bleeding edge' kernel is built, it fails to reboot. I believe this bug was introduced at 5.10.80 or 5.10.81. The kernel I built last night reported itself as 5.10.83-v7+ and was built from commit: 20f6415.
What appears to happen is that the Rpi does not shut down and therefore never reboots. This is after issuing the 'sudo reboot' command from the command line. This is a serious issue with headless devices.