https://www.cnet.com/news/apple-egpu-support-macbook-pro-air-imac/

Apple promised it would let you tap into the power of an external graphics card with your late-model MacBook Pro, iMac Pro and 2017 iMac. That day has arrived: MacOS High Sierra 10.13.4 now officially supports eGPUs, letting you plug a box containing a desktop graphics card into a laptop or all-in-one PC to drastically up its graphics performance and hook up additional monitors.

Technically, the feature had been kinda-sorta enabled in MacOS since High Sierra first launched, but this latest update brings official compatibility for a host of external GPU enclosures and AMD graphics cards, plus the abilities to hot-swap and/or safely disconnect an eGPU by tapping a button in the operating system.