I don’t think it does that if you have Linux on a completely separate drive instead of just a separate partition, but I’m not sure. In any case the solution is just to reinstall grub. Grab a live usb of some linux distro, chroot into your linux install, then grub-install --target=x86_64-efi --efi-directory=/path/to/efi/dir --bootloader-id=GRUB (on uefi, if on bios do whatever the command is for bios, and replace the target architecture with whatever your architecture is, etc)