When a package is removed, but not purged, the configuration files are usually not removed.
dpkg --list | grep ^rc
returns:
rc linux-image-5.11.0-25-generic 5.11.0-25.27~20.04.1 amd64 Signed kernel image generic rc linux-image-5.11.0-27-generic 5.11.0-27.29~20.04.1 amd64 Signed kernel image generic ...
NOTE: The ^rc pattern means that only lines beginning with rc should be output.
dpkg --list | grep ^rc | awk '{ print $2; }'
returns:
linux-image-5.11.0-25-generic linux-image-5.11.0-27-generic ...
sudo apt purge `dpkg --list | grep ^rc | awk '{ print $2; }'`
NOTE: Some warnings may be seen stating that specific directories were not removed.