Getting windows going again after arch was a major nightmare. I installed arch MBR and I think my windows was MBR but I just couldn't get it to boot. I ran across this great post:
How to Repair EFI/GPT Bootloader on Windows 10 or 11 | Windows OS Hub
That made me think about just using EFI. I managed to convert my partition table without destroying anything, but I wrecked my arch boot of course. Many attempts at fixing it were erroring out. What I didn't understand properly is that when you boot from USB to fix whatever boot problem you are having, you have to boot the USB in efi mode. If you don't, you don't have access to the variables stored in the bios non volatile memory.
Once I figured that out I could see the nvram variables and it showed a path to the windows boot loader. I checked and it was missing so I just searched the whole drive for it, found it off in windows somewhere, and copied it by hand into the EFI partition. I really didn't expect that to work but it did
On the arch side, EFI stuff is very very confusing. The wiki seems to indicate that mounting the EFI partition to /boot is the way to go. I have it like this right now but when I did a kernel update, all the kernel stuff failed to handle the path changes.
Like normally if you have a normal /boot, the kernel stuff is right in there. The initramfs and all that. But if you have the EFI partition mounted the kernel stuff goes in like EFI/arch/, so the kernel updates fail.
Also mounting there covers up stuff like /boot/grub so you can't update grub without umounting the efi stuff. This all seems like stuff I'm going to forget in about a week.
Another odd thing is, when grub starts, the efi stuff isn't mounted in /boot, but somehow it finds and uses the kernel stuff in there. But the grub.cfg is in the usual spot. If you put it in with the efi stuff it doesn't use it.
So yea, very confused. I think I might just try one of the other recommended stuff in the wiki, like mounting to /efi and rigging up some kind of trigger to copy the kernel stuff where it needs to go.
Speakin of grub check out the anime butts grub theme I made!