MacBook USB-C Video Out
Apple's USB Type-C Digital AV Multiport Adapter does not display video out until macOS is booted. This adapter is tested and displays the EFI portion of boot so you can see the Apple symbol and the FileVault screen. It is a HDMI 2.0 adapter so it also supports 4K/60Hz display. Disconnect the internal display and use the linked adapter to determine if the MacBook is outputting video.