It appears you're attempting to install a package that isn't available anymore.
As you look for software you have to pay close attention to which version of the OS it is aimed for.
If there is no direct mention of the OS version, then look for the AGE of the information (e.g. "posted ").
Old versions of software has a tendency to not work with a recent OS distribution.
Old software may get replaced entire by something "new", or the setup might require a different style than what you're reading about.
How quickly that happens - and the "severity" of it - depends on changes taking place;
e.g. Ubuntu 16.04 LTS and 20.04 LTS are quite different in setup, due to decisions taken by those involved in the process of creating the later distribution.
Between those there are several actual differences; one such (not related to the Q) is the fact that python2 was dropped entirely. Packages relying solely on python 2 will not work in 20.04.