Hi,
you could check for obsolete packages, depending on the apt version, with
$ apt list '~o'
Also looking for broken or garbage packets could help:
$ apt list '~b' '~g'
Of course, the output will depend on how your sources file
(/etc/apt/sources.list, etc.) looks like.
If you think there could be a discrepancy between the list of packages known to
dpkg and apt, you could test with something like this one-liner
$ dpkg --get-selections | awk '{gsub(":amd64","") ; print $1}' |
(apt list '~i' | awk -F'/' 'FNR > 1 {print $1}' | sort | diff /dev/fd/5 -)
5<&0
Regards,
Jörg.
