In my files, I've included a DVMT script.
Modify the grub.cfg with textedit
Change setup_var 0x432 0x3 to setup_var 0x432 0x4
Save the file
Go to your BIOS, add new boot Option. Call it DVMT or whatever, point to /EFI/Boot/DVMT/bootx64.efi
On boot, press 12 and select the new boot option DVMT
On the Grub Shell GUI, select the 1st option
This will disable the dGPU, change DMVT to 128MB, and enable switchable graphics
This will reboot the computer automatically to make the changes. Boot to MacOS and test.
With the changes, you may disable these in the Config file. Add # infront incase you may want to re-enable and not have to re-add
framebuffer-fbmem
framebuffer-stolenmem