To list all the installed apt in linux you can use
apt list --installed.
A great way to make this command more powerful is to combine it with
apt list --installed | grep gcalcli
WARNING: apt does not have a stable CLI interface. Use with caution in scripts.
gcalcli/bionic,bionic,now 4.0.0~a3-1 all [installed]
Entering this command will list all packages which contain the text gcalcli