I would consider my hardware setup mangled and bizarre. I am trying to get windows to boot from grub. It works just fine from EFI boot menu, though for some reason the EFI system partition is a normal NTFS system reserved instead, presumably because the latest bios I've flashed allows windows to use EFIbootmgr, since there is no clear reason Windows 10 would use BIOS mode. Grub does not indicate that a windows partition has been detected, although a menu entry does appear. I get the standard NTLDR NOT FOUND from other versions of this issue after disabling secure boot.

I would consider this a critical issue since I want this fixed before I try and add in another Linux distro and maybe a thumbdrive BSD. I am playing around a bit with Gentoo and sometimes it silently corrupts itself on my hardware, which requires that I backup the distro system and wipe my SSD. A few well-maintained NTFS partitions simplifies that process significantly. I have Ubuntu mostly out of vanity because the Gentoo installer won't mount efivar under sys and Ubuntu reliabily has them. I forget why that is required but I spent a few days in Fail because I didn't have that. Also just having a simple bootloader from a working distro is needed since the Gentleman seems to disagree often.

Hardware is ASUS z97-P Bios 2906 // Sandisk SSD Extreme 2 (2x [Windows/Gentoo]) 80Gb HDD (UBUNTU) 232Gb HDD (Archival)

Sounds like my gaming box I built.
If the system partition is NTFS, Win10 is in "legacy" (aka CSM) mode.
I had a Win7 system that wouldn't install to gpt, even on a new UEFI m/board (OEM 64-bit pro version as I built the system myself). Now after upgrade Win10 is also still on a MBR disk, and can't be seen from grub which is on a gpt SSD.

Never found a workaround, so basically get used to selecting from the UEFI menu. I use Win10 so rarely it doesn't bother me.

BTW: that NTLDR not found is coming from the "BIOS", not grub.

1 members found this post helpful.

I have to use the CSM else the machine won't even POST. I get another version of the NTLDR not found when I tried to modify it to presumably be compatible with the grub module. I can't say I like any of this nonsense, but really I haven't had a computer do what I wanted for the entire time I have known they existed and that I could use them. Something recent caused the machine not to post until I disconnected some of the SATA devices, and at the moment emerge is doing its usual stubbornness of refusing to sync and then saying its outdated. I suppose it will try to upgrade python again if it does start working, but I can't really chroot from a working distro if it happens to be on a discon'd drive.. Thumb drive also not always an option since sometimes it won't boot if too many USB devices are connected, and it can't always tell that it isn't using the M.2 slot. I am tempted to use a disk-vm from Windows but that is one of the ways I corrupted an OS, because one of the VM managers I use won't let me discard the state. I don't intend on spending another week reinstalling Windows and all the programs I put on it just for a more compatible EFIsys but if it means not spending a month on everything spontaneously breaking I could cope with that.