It's not clear if you've installed Ubuntu in BIOS/CSM/legacy mode or if you're saying you haven't yet installed it but that you can boot the installer in BIOS mode.
If you want to boot the installer, either to install directly or to run Boot Repair, you must find your EFI's built-in boot manager. In most cases, this can be accessed by hitting a function key early in the boot process, but which one is completely non-standardized. (Some computers also use some other key, like Esc.) When it comes up, it will usually have two options for external media, one of which includes the string "UEFI" and the other of which does not. Select the "UEFI" option to boot in that mode and the other one to boot in BIOS/CSM/legacy mode.
In some cases, you may need to enter the firmware setup utility to disable its "fast start" feature (or words to that effect; again there's no standardization) in order for the boot manager to become available.
Also, note that only the 64-bit version of Ubuntu has an EFI boot loader. The 32-bit (x86) version lacks an EFI boot loader and so is not bootable in EFI mode unless you add an EFI boot loader of your own -- and installing the 32-bit Ubuntu on a system with a 64-bit EFI adds another layer of trickiness, so I do not recommend going that route.
Secure Boot should not be an issue, but sometimes it is, so disabling Secure Boot may be worth doing if you try other things and still can't get it to work.
As a general rule, you should not perform a BIOS/CSM/legacy-mode install of Ubuntu on a computer that already has Windows booting in EFI/UEFI mode. If you've already installed in this way, you pretty much must get the Ubuntu installer booted again in EFI mode, either to run Boot Repair or to re-install Ubuntu. The other option is to install an EFI boot loader in some other way. For instance, you could use the USB flash drive version of my rEFInd boot manager to boot Ubuntu in EFI mode, then either switch from the BIOS-mode GRUB (
grub-pc) to EFI-mode GRUB (
grub-efi) or install rEFInd to the hard disk via the Debian package or PPA.
Your Boot Repair output looks correct, at least at first glance. Chances are the firmware on your computer is defective. I recommend you try going to the manufacturer's site and updating the firmware. (The manufacturer probably calls the firmware a "BIOS," although technically it isn't a BIOS.) If that fails, I recommend you return the motherboard and buy a new one from a different manufacturer, since you shouldn't be accepting defective merchandise. (Note that the defect is something that would be in all motherboards of that model with the same firmware version; I'm not talking about a sample-specific manufacturing defect.) If you return the computer, be sure to tell the manufacturer why you did so. They'll keep delivering junk if people keep accepting it; and if you don't tell them why you returned junk, they won't know what needs fixing.
If you really MUST keep that motherboard, you can work around the problem as follows:
- Boot an Ubuntu emergency disk.
/dev/sda1 somewhere convenient -- say,
sudo cp -r /mnt/EFI/ubuntu /mnt/EFI/BOOT.
sudo mv /mnt/efi/BOOT/shimx64.efi /mnt/efi/BOOT/bootx64.efi.
This procedure copies the boot loader to the fallback filename, which the firmware should launch when it fails to launch it under the name registered in NVRAM. This workaround, however, means that GRUB updates (that is, updates to GRUB, not updates to GRUB's configuration) won't be fully installed unless you repeat these steps.
.isofile into a bootable USB flash drive, that tool might or might not copy the EFI boot loader to the USB flash drive. Even if the
EFI/BOOT/bootx64.efifile seems to be present, an EFI might not like some detail of how the USB drive was prepared (like its partition table). Trying another tool may be necessary. Rufus generally does a good job of this. I provide additional comments on this at the end of my CSM page, referenced below.
Note that disabling Secure Boot is seldom necessary. Ubuntu supports Secure Boot, and it normally works fine. There are rare cases of incompatibility because of bugs in the EFI and/or in an Ubuntu component, but these normally cause the Ubuntu installer to fail to boot. Secure Boot can also complicate use of some third-party drivers after booting.
For more information on this subject, I recommend you read: