Your package has a preinst maintainer script, calling adduser. At the same
time, your package Depends: adduser, but does not Pre-Depends: adduser.
Also, the preinst silently ignores failures from adduser (with
"2>/dev/null || true").

As a result, the dpkg-statoverride call after adduser fails.

Reproducer:

$ mmdebstrap --variant=essential --include=ganglia-monitor unstable /dev/null
...
Selecting previously unselected package ganglia-monitor.
Preparing to unpack .../20-ganglia-monitor_3.7.2-7_arm64.deb ...
dpkg-statoverride: error: user 'ganglia' does not exist
dpkg: error processing archive /tmp/apt-dpkg-install-rKdVwf/20-ganglia-monitor_3.7.2-7_arm64.deb (--unpack):
 new ganglia-monitor package pre-installation script subprocess returned error exit status 2
Errors were encountered while processing:
 /tmp/apt-dpkg-install-rKdVwf/20-ganglia-monitor_3.7.2-7_arm64.deb
E: Sub-process env returned an error code (1)



You may consider replacing adduser with a sysusers fragment, see
https://manpages.debian.org/unstable/debhelper/dh_installsysusers.1.en.html

Otherwise, please Pre-Depend on adduser.

Best,
Chris