In this thread https://mail.coreboot.org/hyperkitty/list/coreboot@coreboot.org/thread/FTHN5... we found a bug in seabios. Its choosing the wrong option rom in the case when for example on a Intel G41 board you have the internal Intel GPU and have added a external PCIe GPU. Then coreboot switches over to the external GPU for the graphical output but seabios use the option rom for the Intel G41 GPU. In case of x4x/G41 this results in no ability to have a graphical boot mode and thus its not possible to boot some linux live images. In the linked thread a workaround is been found: "In the "Devices" menu of coreboot, set "Graphics initialization" to "None" ". This breaks the functionality to have coreboot output with the internal GPU when you pull out the PCIe GPU. The switch should happen automaticly and without the need to recompile/reconfigure coreboot. Changes like https://review.coreboot.org/c/coreboot/+/18504 was made to make this happen.
Would be great if this seabios issue could be fixes. Thanks!