For Bootcamp Windows internal screen, it’s much harder. I followed the instructions from egpu.io, and it worked. Now I can play Overwatch at high setting and 60 fps (because retina screen only supports 60 Hz). Had to use a bluetooth mouse (not a 2.4G) as the egpu uses up all the PCIE bandwidth, that any pluggable mouse wouldn’t work.

https://www.amazon.com/GIGABYTE-Gaming-Graphic-Card-GV-RX580IXEB-8GD/dp/B07CCK527Y