Mac touch-id turned off, can't turn on
Yesterday, touch-id stopped working on my M1 iMac with Ventura 13.0.1.
I went to "System Settings", "Touch ID & Password" and tried to slide the switch on, but the slider was greyed out, I couldn't turn it on. It appears to still know about my fingerprint.
How do I turn it back on the way it has been for a year and a half?
iMac 24″, macOS 13.0