You should be able to boot Mojave with the USB Install Disk and the HDMI cable.
Once you login, mount EFI partition on Mojave SSD and backup the current config.plist.
Then copy the attached version.
Open it with Clover Configurator first to make sure no errors are reported during the file-open process. If so, quit Clover Configurator.
Then reboot (again with HDMI to HDMI cable) normally from the Mojave disk (remove USB install disk).
Does the black screen problem go away?
This config.plist contains framebuffer patching code that reorders the BusIDs for DP and HDMI. It's from forum member nor500 who has a similar motherboard (H370
M-DS3H), so hopefully this will work for you.
Also please be aware of some hot-plug issues:
https://www.tonymacx86.com/threads/...uhd-630-on-i3-8100.268270/page-6#post-1887556