To my recollection on the machines that shipped with Lion (circa 2011) you’ll want to set up a protective MBR with the appropriate drive dimensions on the GPT, to get it to install windows like with boot camp.

To my recollection on machines with discrete GPUs this is what triggers the appropriate hardware configuration (BIOS boot, disabling the internal GPU and switching the MUX to only route via the AMD card)

But I do recall getting the internal GPU working with this trick https://github.com/0xbb/apple_set_os.efi