I had the exact same problem with regular Fedora KDE. In my case it turned out that it didn’t wipe out the entire Microsoft bootloader because there was a backup bootx64.efi. In the end I downloaded a windows installer iso, copied the boot* files and directory to efi/Microsoft/boot and copied that bootx64.efi and added it to the grub menu using the 40_custom file in grub.d and applied grub2-mkconfig -o /boot/grub2/grub.cfg
To boot from grub you use set root and chainloader /... which you then write as a menuentry
Sorry for the bad reply but I’m working
I hadn’t read the other drive stuff. I’m guessing it’s the same case as mine since you planned or guessed you would be using Grub on your primary drive instead of Windows boot manager. I don’t have my computer with me but I would be willing to make a more concrete “tutorial”. You can DM me too