Network works, NetworkManager sees nil, PackageKit offline

This article should make you reflect on the concepts of the Linux desktop. GUI and simplicity of software, all together. 'Tis a tutorial on how to resolve the bogus problem of system being supposedly offline as reported by the KDE Discover package manager in Ubuntu-based Plasma desktop, including overview of the problem and blind reliance of the toolchain on PackageKit and NetworkManager for network connectivity without any checks, clash between desktop and server functionality and use of netplan and its YAML-formatted recipes for networking, deferral of network management to NetworkManager for network connectivity, problems with pseudo-security in using sudo with text editors in the Plasma desktop, some other tips and tricks, and more. Enjoy.