As soon as he said that, I was silent, as I have not have had an MBR scheme disk in ages.
But the os-prober malfunctions on MBR Windows do seem abundant searching around. Especially with NVMe drives.
But where I was going for earlier, is using a /etc/grub.d/.. way. (And disabling os-prober.)
Depending how comfortable @Umbra_noctis is. There is a way you can test this first in the clunky grub command line (from hitting c upon booting). But it’s a little easier, to just attempt to boot your own menu entry. Which I believe should look like this for you..
e.g.: /etc/grub.d/50-windows-mbr
#!/bin/sh
exec tail -n +3 $0
menuentry "Windows 10 (Legacy MBR)" {
insmod part_msdos
insmod ntfs
search --no-floppy --fs-uuid --set=root 707C2F317C2EF190
chainloader +1
}
I just simplified, figured that’s a good start.