As a (poor) workaround you can use these commands (in a the terminal) to activate an external display:
xcrun simctl io booted screenConfig --display=2 power on
xcrun simctl io booted screenConfig --display=2 geometry 1920x1080
(Make sure only one device is booted, or replace "booted" with the simulator ID).
Then whenever you need to see what is on the external display:
xcrun simctl io booted screenshot --display=2 screenshot.png
Topic:
Developer Tools & Services
SubTopic:
Xcode