For LOS 16.0, the usual string shown there was "Builtin Keyboard".
I'd say, either the keyboard is indeed physically disconnected, or the system has been re-configured to default to some other hw keyboard. Did you ever use an external USB or Bluetooth keyboard in the past? If yes, what happens if you re-connect that?
However, as your problem appeared kind of gradually, I rather fear that the keyboard is indeed not properly connected to the system board anymore. Maybe the ribbon cable connecting it to the board has loosened with time. There is a quite complete official disassembling g