i see opencore legacy patcher and have fix for this gpu in new system
https://www.insanelymac.com/forum/topic/348122-graphics-acceleration-for-amd-terascale-2-cards-eg-ati-radeon-hd-5770-now-possible-in-big-sur/
i think in. this case dont work
u need put one amd card like rx560 or + and use macpro7,1 smbios
remove ssdts u dont need it, use only dsdt and ssdt uiac for usb remap