They may have pointed to the wrong installer file for the latest release. Click on the Archive menu and then either Windows or Mac OS X link next to the Unity 2018.1 Magic Leap Technical Preview Release 9.
I’m having the same issue, I have the latest Unity which is Version 2018.3.4f,1 Lumin SDK is already installed from Magic Leap Package Manager. Magic Leap option is not showing up in template. Please help and thanks in advance