From CMOS Battery Reset.
Power off system and unplug power cables
Press and hold power button for 30 seconds
Remove CMOS battery
Press and hold power button for 30 seconds, again
Put CMOS battery back, plug system back in, power system back on (or it powers on as you plug it in, because sometimes barebones does that)
Splash screen shows up <1 minute with minimal POST (+1x GPU) installed on Onboard (front VGA port) display.
In short, remove the VGA port, and plug in the display to the Graphics Card. Having both plugged in will result in only splash screen on VGA and nothing past that on any other display-capable device installed to the motherboard. EDIT 7/2/21: Having both displays SOMETIMES work.
This motherboard in particular DOES NOT support display auto-switching, meaning if it fails to output proper display through sequential hardware initialization (during POST, detecting display devices and cable to monitor), then it will just never display anything past the splash screen at all; if you missed it, or did this incorrectly, you will need to press+hold the power button for 5 seconds to power off the system and start over by powering the system back on so it can go through POST again.
If you plug in VGA cable, AND the 'Primary Video' setting in BIOS is set to use 'PCIe Device', then you will be met with this 'DXE-Setup Input Wait' screen with 'AB' code on the bottom-right. This is consistent, so no-display with any other code might indiciate an issue with BIOS or motherboard.