Funny you should mention this, I just created a user on a debian 10 VM 3 days ago.
CFEngine is hard coded to /sbin/useradd regardless of community or enterprise version.
config.h <global> 1111 #define USERADD "/sbin/useradd"
I have a symlink from usr/sbin to sbin, so maybe that is broken in your debian installation?
lrwxrwxrwx 1 root root 8 May 10 07:26 sbin -> usr/sbin
> This page tracks Debian support for the merged /usr directories scheme, i.e. the /{bin,sbin,lib}/ directories becoming symbolic links to /usr/{bin,sbin,lib}/.
Looking forward to figuring out what's going on for you,
Craig