CPU: AMD Ryzen 7950X3D
Mobo: Gigabyte X670e Aorus Master Rev.1 / MSI MPG X670e Carbon WiFi Rev.1
dGPU: AMD Radeon RX 6900XT reference
BIOS version: F10c (GB) / 7D70v172 (MSI)
BIOS settings for Gigabyte:
Settings > IO Ports > Initial Display Output > IGD Video
Settings > IO Ports > Integrated Graphics > Forced
When a cable is connected to any DP/HDMI ports of dGPU, bootloader ignores iGPU and sets dGPU as initial display. This happens even if the monitor is switched off or not connected at all (cable only on dGPU side). Removing the cable from dGPU during boot, and adding it later, works as intended.
This results in OS loading in dGPU instead of iGPU.
Tested with Windows 10/11 and 3 Linux distros (Manjaro, EndeavourOS, Kubuntu)