To use the HDMI port on the rear IO panel of the motherboard, please backup your existing config.plist and try the attached version. This version does the following:
- Sets Platform ID to 0x3E9B0007 to drive a display monitor
- Sets framebuffer patches to enable the on-board HDMI port
Then connect display monitor to HDMI port on the back of the motherboard, and reboot.
- Set Internal Graphics to enabled (not auto)
- Set Initial Display Output to IGFX
You may also remove the RX 580 because that card will not be used properly. You can either (a) replace it with standard RX 580 or (b) flash a new standard VBIOS.