Running system mono/msbuild, ERROR: Invalid SDK MacOSX.sdk, not found in /Library/Developer/CommandLineTools/Platforms/MacOSX.platform/Developer/SDKs
Turns out there’s a setting
in Xcode’s preferences
under Locations which needs to be turned on.
The part in the image called ‘Command Line Tools:’
was blank, so I toggled on the only option available.
I tried creating a new project and it worked.