For Maxwell/Pascal (unsupported in Mojave+), consider switching to AMD or Intel iGPU.
A GUI tool to edit your config.plist and mount EFI partitions.
macOS defaults to the iGPU for initial boot processes. If your HDMI monitor is plugged into the dGPU, you might get a black screen because the handoff between the iGPU and dGPU failed.
