il2cpp isn't available on the Scripting Backend setting

I want to try compiling a Windows binary in il2cpp, but on the Windows/Mac/Linux build settings panel my Scripting Backend setting only contains Mono2x and not il2cpp. I thought this might be because I was missing an Unity component, but on the last update I selected every optional package on the installer, and it still isn't there. Can anyone explain why this might be? ![alt settings pannel][1] [1]: /storage/temp/62646-backendsetting.jpg