Pi-hole error installing in ubuntu 18.04.3

The above command fails because you didn't tell apt which package to install; you gave a version number rather than a package name.

I'm wondering if something is wrong with your package manager. What happens when you try to manually install the dependencies?

sudo apt install libssl1.1 php7.2-cgi php7.2-sqlite3

Please post the output you get from running the above command. If it succeeds, then re-try the apt command you saw in the logs:

sudo apt install netcat idn2 sqlite3 lighttpd php-common php-cgi php-sqlite3