list of installed packages on Debian

#list all installed packages with dpkg
dpkg --get-selections| grep -v deinstall
#get a count of installed packages
dpkg --get-selections| grep -v deinstall|sc -l

#list all installed with apt
apt list --installed
#get a count with apt
apt list --installed|grep -v "^Listing"|sc -l

###backup list of installed packages###
dpkg --get-selections | grep -v deinstall > packages.lst
sudo apt-get install -y $(< packages.lst)
sudo apt-get autoremove