Maybe to fix this PCIe GPU issue he just needs to edit a ./coreboot/src/device/Kconfig file?

./coreboot/src/device/Kconfig
change

config MULTIPLE_VGA_ADAPTERS
   bool
   default n

to

config MULTIPLE_VGA_ADAPTERS
   bool
   default y

and completely rebuild the coreboot

I enabled these options for my G505S laptop with both integrated/discrete graphic, however I am not a gamer so can't notice if there is any positive effect from this option. But maybe this option will significantly improve the thread starter's eGPU experience? What do you think ?