Great news! /u/QubesN00b flashed this dGPU build to his "no-dGPU" G505S and everything seems to be working fine for him :D ( https://www.reddit.com/r/coreboot/comments/ar8v7d/if_your_g505s_does_not_hav... ) . Now I could e.g. remove "if (IS_ENABLED(CONFIG_MULTIPLE_VGA_ADAPTERS))" condition from https://review.coreboot.org/c/coreboot/+/31450/3/src/mainboard/lenovo/g505s/... - and set BottomIo to 0xD0 for all G505S.