Did anyone end up figuring this out? This is working fine on one of my machines, but not another. There are some suspicious parts of the log on the non working machine
default 09:18:10.075726-0400 mobileactivationd Client certification requested by CarPlay Simulator
error 09:18:10.088862-0400 CarPlay Simulator Failed to obtain valid certificates from server: <private>
error 09:18:10.103753-0400 CarPlay Simulator Incoming message ID 0xaa04 AuthenticationFailed
and
error 09:18:09.452387-0400 CarPlaySimulatorDeviceLink RemotePairing.framework is not available.
default 09:18:09.452419-0400 CarPlaySimulatorDeviceLink RemotePairing.framework not found.
Meanwhile the working machine according to Activity Monitor is loading /Library/Apple/System/Library/PrivateFrameworks/RemotePairing.framework/Versions/A/RemotePairing just fine. The non working machine does have that file on disk.