I added modules for Linux and Mac in Unity Hub but in Unity the only option for Target Platform is still Windows. I tried closing and reopening Unity. I am using Unity 2018.2.11f1. My selected platform is PC, Mac & Linux Standalone. The only searches I could find where people had the same problem it was resolved by adding the modules (but I have already done that). I am grateful for any assistance.
Nevermind. It turns out the modules were installed to a different version of Unity and the Unity version I was running was not listed in Unity Hub. I uninstalled all versions of Unity and Unity Hub and deleted the version of Unity that was not listed in appwiz.cpl and started fresh. Now I see the other options in the dropdown.