Why does GRUB behave like this?

Question

GRUB

Good afternoon, linuxoids! I need your help, I'm already tormented. There is Windows 10, on a 1TB hard drive, there is also a 250GB hard drive. where i installed linux mint. Everything was fine, but I have been suffering with the GRUB problem for a long time.
I installed Linux Mint, everything is fine, I restart the computer, there is GRUB, I select Linux - Loads.
Then I turn it off, I choose Windows - it also loads. Everything seems to be fine, but
after that I turn off Windows, and GRUB no longer appears, Windows starts automatically, I also tried to start it through the Boot Device, immediately 250GB. disk, but there was some error with DHCP, not quite understood.
I think well, Windows loads. I take out a 250GB disk, and after that Windows also does not boot, and GRUB also appears as a console, without a graph. shells. And in the BIOS, after removing the 250GB hard drive. my "Windows Boot Manager" now shows up as UBUNTU. I didn’t understand anything, I inserted a 250GB hard drive. back, and GRUB appeared! But that's just all over again. Linux booted, Windows too, but next time GRUB is gone again. Linux Mint installed on 250GB. the disk completely, that is, cleared it, and let Mint do everything on it, (It seems like there are 2 partitions: "EFI" and another one ...). I also installed it on a laptop on one hard drive next to Windows, everything works smoothly there, but for some reason it doesn’t work at my bakery. I ask for help, I tried to restore GRUB using "chroot" and some other way, but it does not help,

Answer 1

The reason for your problems is windows 10, which restores the boot sector on its own initiative.
The windows bootloader must be installed on a 1tb disk, and grub on 250gb, as a bonus you can use the BIOS boot disk selection (by F11 or F12)