I realize this is a commonly asked question but I think my situation is a little unique.
I have an old i7 920 that I'm dual booting with Windows 10 and Linux Mint 19.3 Cinnamon. In order to install Windows, I had to enable UEFI booting in BIOS. Windows is installed and I've installed Mint, but it did not install GRUB and now I am unable to boot into Mint. Upon entering live Linux again, I can follow the directions in this thread here to mount /dev/sda6, which is my Linux partition, to /mnt and then bind /dev, /dev/pts, /proc and /sys as directed and then chroot to /mnt. However, when I try to sudo install-grub /dev/sda it says:
Both my Windows and Mint USBs were burned in rufus with mbr. Windows boots just fine. Is there some way to install GRUB on /dev/sda without having to try reinstalling Windows, which I'm not even sure would work? I've tried burning my Mint USB in rufus with GPT but when I try to boot from it it says that it can only boot in UEFI mode (obviously) and that I need to disable or deprioritize legacy boot. My BIOS does not provide this option. If I disable UEFI boot in BIOS, it boot into Mint without giving the option to boot into Windows.grub-install: warning: this GPT partition label contains no BIOS Boot Partition; embedding won't be possible.
grub-install: warning: Embedding is not possible. GRUB can only be installed in this setup by using blocklists. However, blocklists are UNRELIABLE and their use is discouraged.
grub-install: error: will not proceed with blocklists.
Any help is much appreciated. I need this figured out ASAP. Thanks in advance.
EDIT: In Linux I have run sudo update-grub and it updated. I then rebooted it and it would not load anything. It just got stuck with a blinking cursor in the top left. I re-enabled UEFI boot and it is once more booting into Windows. Disabling UEFI boot again once more causes it not to boot. Booting live linux and using chroot to update grub does not fix anything. I'm completely unable to boot into the installed Linux now. I'm going to reinstall it.
EDIT #2: I've reinstalled Linux and I am able to boot into it if I disable UEFI boot in BIOS.
EDIT #3: When I examine the drives in Linux, it looks like the Windows drive is an EFI system partition. I'm not sure how that happened. Am I going to need to reinstall Windows to have GRUB work properly?