So I have an old iMac that I've been trying to get to dual boot Windows 10 and Ubuntu 20. Sadly the Windows 10 installer installs as MBR/BIOS. I converted this with mbr2gpt, which was sorta successful and I was able to install Ubuntu along side it. I am now at this state:

I have a the grub loader working great....I get my menu, and I can choose Ubuntu or Windows. Sadly the above is what I get when I try to boot to Windows. The caveat with trying to repair...I can't seem to get ANY windows usb/cd to boot now. So with that in mind, is there any known way to fix this by mounting the windows partition and fixing a few files? Thanks.