One or more eGPUs can be used with the MacBook Pro 2016 and 2017, the iMac 2017, and the iMac Pro, provided macOS High Sierra 10.13.4 in Apple recommends eGPU support for graphics-intensive operations such as VR headsets, 3D gaming, and the development of VR applications.
Apple's support document describes all supported eGPU configurations, where Apple only recommends AMD Radeon cards. No Nvidia cards are supported.
It is also worth noting that Apple has support for some cards that were supported during the beta, such as the AMD RX 560, apparently discontinued.
It is important to use an eGPU with a recommended graphics card and Thunderbolt 3 chassis. And if you're using a MacBook Pro, the eGPU's Thunderbolt 3 enclosure needs to provide enough power.
Apple recommends AMD Polaris, Vega 56, and Vega 64 graphics cards, paired with a special Thunderbolt 3 package. For the AMD Radeon RX 570, RX 580 and Radeon Pro WX 7100 (of which Apple recommends the Sapphire Pulse Series and the AMD WX Series), Apple recommends the following Thunderbolt 3
OWC Mercury Helios FX3
PowerColor Devil Box
Sonnet eGFX Breakaway Box 350W
Sonnet eGFX Breakaway Box 550W3
Sonnet eGFX Breakaway Box 650W3
Fits the AMD Radeon RX Vega 56 cards Apple recommends the Sapphire Vega 56 and the XFX Vega 56 with the OWC Mercury Helios FX, PowerColor Devil Box, Sonnet eGFX Breakaway Box 550W3 or Sonnet eGFX Breakaway Box 650W3.
The Sonnet eGFX Breakaway Box 650W3 is the only recommended case for the AMD Radeon RX Vega 64, Vega Frontier Edition Air, and Radeon Pro WX 9100 graphics cards, while Sonnet Radeon's only recommended all-in-one eGPU product RX 570 eGFX Breakaway Puck is.
For the MacBook Pro, the eGPUs and the associated TB3 enclosure must provide enough power to power the graphics card while charging the computer. In the case of the 15-inch model, this means that the chassis has to provide at least 85 W of charging power.
Apple says eGPU support has been developed to accelerate metal, OpenGL, and OpenCL applications that benefit from more graphics performance. Not all applications support eGPU acceleration.
Multiple eGPUs can be used together, but Apple recommends users connect eGPUs directly to the Mac instead of concatenating them through another Thunderbolt device or hub.
macOS High Sierra 10.13.4 does not support eGPUs on Windows with Boot Camp or if the Mac is in macOS Recovery mode or if system updates are installed.