This is not for full desktop screen sharing. It allows you to forward the graphical contents of individual windows to your Mac from a remote Linux machine, regardless of whether that machine is connected to a physical display or not.
Steps below based very much on https://unix.stackexchange.com/a/46748
You will need XQuartz, since X11 server is not installed with MacOS after version 10.7
Download here: https://www.xquartz.org/