In macOS, lurking beneath the pretty graphics is a complete Unix operating system based on FreeBSD, including support for X-windows. Most of the open-source software developed for Linux/FreeBSD has been ported to macOS, so for the Unix fans (like me), the operating system can look like Unix with a great graphical interface that also runs Macintosh applications. Overall, macOS is a very impressive desktop/laptop operating system.
The programs built with the GTK graphics toolkit require that an X-windows server be running, as X is used for graphics. This is not installed automatically. The Apple-sponsored X-server is called ``XQuartz'' and is available for download from the project web site (google ``XQuartz download'').
The programs built with the Qt graphics toolkit are native macOS applications and make use of direct access to the s creen, so there is no neew for XQuartz in this case.
Operation and behavior should be identical or very similar to the Unix/Linux versions of the programs.