Although using an external GPU on a MacBook was possible in the past by booting up Windows on it, macOS High Sierra 10.13.4 finally brings native support for external graphics processors to Apple's operating system. This update also contains multiple minor tweaks and fixes, including a fix for the graphics corruption issues encountered in certain apps on the iMac Pro.
https://www.notebookcheck.net/Support-for-external-graphics-cards-finally-available-in-macOS.293664.0.html