I'm missing something about Glade

I have installed and created a working configuration for my mill. I'm very happy with it so far. I previously had the mill controlled by mach4, which had some issues. There were some things that I like about the mach4 gui, though. I want to modify my linuxcnc gui to include some of these features and thought I might be able to use gladeVCP to do it.

The installation I used for linuxcnc is the newest and recommended install. When I follow the gladeVCP documentation section 3.1, which says that if the Glade command is miss, install it with the command sudo apt install glade.

The glade command is indeed missing, but sudo apt install glade fails with unable to locate package glade.

What am I missing? Where can I find the glade package?
 

I solved this problem. When I installed from the .iso, the drives for the computer wifi were not available, so I installed without an internet connection. This evidently creates a system that only mostly works. The apt app was broken. I connected to the the internet with a cable and re-installed the .iso. Now, I've been able to do sudo apt install glade without issue.