I made another partition on my bigsur hdd. I installed clover like this
- Install Clover (v4920 till May,2019) on USB:
--Set install location on USB
--Click Customize, select:
Install at EFI section
Bios0af
BiosBlockIO
drivers64/ApfsDriverLoader.efi
Install RC Scipts to all Bootable partition & Install extra RC Script
This is the only way for it to show up as a legacy device and trigger the 7.
I then added these bios files instead of the correct ones and used a Open core efi. I click second hard drive and it works.
Now this final step is the hardest and I would recommend getting the gray screen to work properly with a USB first.