Hrm, I’m not sure how you are going about your installation procedure. You mentioned that you are installing Ubuntu, but Ubuntu should come with Grub pre packaged. Installing Ubuntu really only requires clicking a couple buttons in the install wizard.
I had Linux installed on a tertiary partition of a secondary drive, my F: drive. I neglected to store it within the dedicated SSD, C:, and I believe that GRUB was just not being picked up because instead of being sda or something close to it, it was instead sda6.
Further this with the fact that GRUB seemed to not have elevated permissions and when I eventually got into its command line, it was not able to run Linux for reasons I’m unaware. Windows BIOS menu never had Linux or any corollary term available as a boot order item, and only through digging through the Boot from EFI item and submenus was I able to find anything to actually boot Ubuntu without live CD at all. grubx.efi (or whatever it was called) black screened.
Im not really familiar with shim, but, from what I understand, it’s the loader for when you have secure boot enabled, but you should have that disabled.
Scout’s honor, I really did disable Secure Boot. I did so through Shell. I did so in the Windows directory. I even triple checked that it was disabled through the BIOS menu. If shimx64.efi is only supposed to work when Secure Boot is disabled, that must be because Windows has just been acting screwy as all get out.