I am no expert on mangos but I believe that you need to select a path to your includes, lib or libpath. You can do this by pressing Advanced options and scroll down until you find it.
I think this should work because this message
To select the path just press the 3 lined dots and select the folder location manually.
CMake Error_ Error SetGlobalGenerator called with null
CMake warning at CMakeLists.txt:14 (project):
To use the NMake generator, cmake must be run from a shell that can use the compiler cl from command line. This envirement does not contain INCLUDE, LIB, or LIBPATH, and these must be set for the cl compiler to work.
/*Note that this is a theory but I think that should be the issue your encountering.*/
Best Regards, Unknown96!