freeglut provides CMake targets:

    find_package(FreeGLUT CONFIG REQUIRED)
    target_link_libraries(main PRIVATE $<IF:$<TARGET_EXISTS:FreeGLUT::freeglut>,FreeGLUT::freeglut,FreeGLUT::freeglut_static>)

freeglut is compatible with built-in CMake targets:

    find_package(GLUT REQUIRED)
    target_link_libraries(main PRIVATE GLUT::GLUT)