Wt

src/Wt/WServerGLWidget.C:24:10: fatal error: GL/gl.h: No such file or directory
   24 | #include <GL/gl.h>
      |          ^~~~~~~~~
compilation terminated.

Google says that there is not GL/gl.h on apple platform.
That file contains also following code

#ifdef APPLE_GL
#include <OpenGL/OpenGL.h>
...

Commenting that include helps.
So include must be under some ifdef.