Have you tried adding this to Windows BCD with Windows bcdEdit?
bcdedit /set {bootmgr} path \EFI\ubuntu\grubx64.efi
Grub only works is secure boot is off. Not sure if shimx64.efi would work from Windows with secure boot on or not.
Many systems need work arounds as vendors/mfgs violate UEFI standards and use description as part of UEFI boot. And only description allowed is "Windows". In those cases another work around is to copy grubx64.efi or shimx64.efi into /EFI/Boot and rename to bootx64.efi. Then in UEFI select hard drive as boot option.
Have you tried adding this to Windows BCD with Windows bcdEdit? grubx64. efi
bcdedit /set {bootmgr} path \EFI\ubuntu\
Grub only works is secure boot is off. Not sure if shimx64.efi would work from Windows with secure boot on or not.
Many systems need work arounds as vendors/mfgs violate UEFI standards and use description as part of UEFI boot. And only description allowed is "Windows". In those cases another work around is to copy grubx64.efi or shimx64.efi into /EFI/Boot and rename to bootx64.efi. Then in UEFI select hard drive as boot option.