CMake (not make) is a project configuration tool that can generate Makefiles from it’s own configuration, and there is a such thing as cmake-gui.
It’s indeed in extra/cmake package. Maybe try to specify full path in terminal (/usr/bin/cmake-gui)?
$ pacman -Ql cmake | grep gui
cmake /usr/bin/cmake-gui
cmake /usr/share/applications/cmake-gui.desktop
cmake /usr/share/cmake-3.20/Help/manual/cmake-gui.1.rst
cmake /usr/share/man/man1/cmake-gui.1.gz