Our company has an internet-isolated environment, and I was requested to create a WSUS infrastructure there.
The most annoying thing about installing a disconnected WSUS server is that you can't do it via the server manager (because it requires a working internet connection) but rather through an exe file, and that file won't install the prerequisites, just complain that some of them are missing (without informing you which ones), compared to the automatic prerequisite installation of the server manager.
Well, problem solved through the power of scripting!
The following line of code will install all of WSUS's windows-related components without actually installing WSUS through the ServerManager module:

ipmo ServerManager;
Get-WindowsFeature OOB-WSUS | select -exp DependsOn | Add-WindowsFeature