But this is the Windows XP group.
There is a separate group for Windows-10.
Perhaps there is a slight misinterpretation of what's happened ?
First of all, the BIOS has a popup boot menu. It has *multiple*
entries in it. This serves to prevent a loss of control incident.
Windows Boot Manager is one entry. Ubuntu can be a second UEFI entry.
The BIOS offers your "first level" of boot selection.
Windows 10, when it does an upgrade, some of the more recent ones
(like maybe 19041), they may change the previous "Win10" "Win7"
BCD menu to just "Win10", then, since a BCD with only one OS does
not need to present a menu, selecting "Windows Boot Manager"
causes immediate boot into Windows 10. This piggish behavior
can be stopped by using Macrium Reflect Free CD "fix boot problems"
entry, which will put Windows 7 back into the BCD for you. While
EasyBCD can also be used for this sort of work, it depends on which
version you've got, as to how well it will work.
On upgrade installs, Windows 10 does not remove other OSes. It has
a nasty habit of creating an extra 500MB partition with a WinRE.wim
inside it. But normally, since much of GRUB uses blkid/guid, this
does not break anything. This was not an "intentional" attempt to
break GRUB. Microsoft is perfectly capable of erasing all the
folders in the ESP, as any OS can, and they are simply not doing that.
There is no need to launch everything via GRUB. You can select
Windows Boot Manager from popup boot in the BIOS. You can also
select Ubuntu, and chainload a specific Windows OS from there.
That means there are at least two ways to launch a Windows OS.
But you are not limited to just using GRUB on a UEFI machine.
There are two steering wheels.
However, what you have to be aware of, is even though a lot of
things work with GUID or BLKID, sometimes removing or adding
a single partition, can upset something which is still using
a partition number or a drive letter for its boot menu. In other
words, a change you made to the disk lineup yourself, might actually
have resulted in a boot failure.
DATA WIN10 UBUNTU
If you remove the DATA partition, that will break your boot.
I think I found something in the Ubuntu folder in the ESP,
which points to a particular partition number.
To access the ESP easily, you can try the following.
1) dd copy the ESP FAT partition to a separate .img file.
The ESP might be the first partition. "gnome-disks" can help
you get the sda1 part right.
sudo dd if=/dev/sda1 of=esp.img
2) loopback mount it
sudo mount -t vfat -o loop esp.img /mnt/somefolder
3) Now you can use nemo or the like, to look inside.
My recollection is, there was some grub file in the Ubuntu
folder, with a partition number reference. One of those
(HD2,0) type things.
It's been a while since I've had to reinstall grub as
a Houdini thing. I don't use Boot Repair, because its
track record is not perfect. There is always chrooting
from live media. Using the keyword "chroot" you can
usually find a list of what mounts to use.
One of the golden rules of multiboot, is to not have
more than the target disk in the machine, when installing
OSes or fixing boot. This prevents inadvertent "linkage"
to the other disk drives in the computer. You can unplug the SATA
cabling from the excess disks, before starting your surgery.