External display adapters support

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Background: all USBC MacBooks support external screens, however it is not that easy to get a picture on Filevault login / Recovery / Boot menu. The problem is that USBC Display negotiation starts only after GPU driver is loaded, which will never happen if you are not able to click on your password field and type password. The common technique is to physically disconnect internal screen and to fiddle with connectors till something works. However on some T2 models it looks like even then, there might be no external picture. This issue looks pretty obscure and funny but i see no better way but to test every device i have my hands on and to build up a table with known-good cable combinations. To do the trick, connect external keyboard/mouse, turn on the device and immidiately close the lid. Boot logo should appear on external screen even before the Filevault login.


MacBook 13" with integrated Intel GPU

USBC-DP (Cable Matters USB C Mini DisplayPort) as DP1 in table(add your cables)

USBC-HDMI (Uni USB C to HDMI) as HDMI1

USBC HUB (Anker 8-in-1 USB-C Hub) + normal HDMI-HDMI Cable as HUB1

This table indicates MAIN image on external screen with internal screen PRESENT
Device USBC > DisplayPort USBC > HDMI USBC > USBC USBC HUB with HDMI/DP/Etc
MacBook 2016-2017A1708/A1706 DP1 X X HUB1
MacBook 2018-2019 A1989 DP1 X X HUB1