Debian will be back up in about an hour.  I identified the problem as a bug in systemd-sysusers which causes it to hang if NIS is used with containers and avahi is not present.

      Avahi is not present because I do not want it “discovering” potentially insecure machines on the network and prefer the machine knows only about what I tell it.

      Since NIS is not optional and snap is, I’ve removed snap and that made Debian boot properly.  I am now making a backup to capture the current working configuration.  That will conclude in about an hour at which point the machine will be returned to service.