Grub2 problem with Tumbleweed installation - "Function not implemented"

I’m trying to install Tumbleweed on a Dell Optiplex 7020 system that previously had OpenSuse Leap 15.0. During the installation, I get an error that says:

Execution of command ""/usr/sbin/grub2-install","--target=x86_64-efi"'"--
force"'"--skip-fs-probe"]]" failed.
Exit code" 1
Error output: Installing for x86_64-efi platform.
Could not prepare Boot variable: Function not implemented
/usr/sbin/grub2-install: error: efibootmgr failed to register the boot entry: Input/
output error.

I can boot into Tumbleweed on this machine if I use the installation media to select Tumbleweed. Opensuse Leap 15.0 also remains on the system, and I can boot into it through Grub2. I won’t need Leap 15.0 any more once I get Tumbleweed working properly. I’ve had a few versions of OpenSuse Leap on this machine, and I never had issues with Grub2. What can I do to configure Grub2 to boot Tumbleweed on this system?

Go into Yast Bootloader.

There should be a box: Update NVRAM Entry

Try unchecking that box, and see if it will install grub properly that way.

The issue is with efibootmgr, not with grub2. You can run “grub2-install --verbose” which should print efibootmgr invocation and then call the same efibootmgr command adding several times "-v -v -v " to increase verbosity. Chances are it provides better diagnostic. Upload full output to https://susepaste.org

I posted the output of efibootmgr -v -v -v at https://susepaste.org/19774817

That is not what I requested.

Please see this output: https://susepaste.org/81063645

As nrickert recommended you should try

grub-install --no-nvram
efibootmgr -c -d /dev/sda -p 8 -w -L opensuse -l \EFI\opensuse\grubx64.efi.

Well, show results of

fdisk -l /dev/sda
findmnt
efibootmgr -c -d /dev/sda -p 8 -w -L opensuse -l \EFI\opensuse\grubx64.efi. -v -v -v

Sorry, copy-paste issue, there is extraneous dot in file name. The correct command is of course

efibootmgr -c -d /dev/sda -p 8 -w -L opensuse -l \EFI\opensuse\grubx64.efi -v -v -v

This will copy grub to ESP \EFI\opensuse (which it already did) and won’t add boot entry to firmware boot manager (which it already did not). So what exact difference will it make? If anything

grub2-install --removable

may work by copying grub into \EFI\Boot directory. Of course this will overwrite existing bootloader there, so one needs to have contingency plan how to restore old files.

P.S. it is grub2-install on SUSE.

I got Grub2 working for Tumbleweed. I reinstalled Tumbleweed and had it delete old Linux partitions since I don’t need the OpenSuse Leap versions that were still on the drive. I disabled the Update NVRAM option during the installation. I had to choose Grub2 instead of Grub2-EFI for Grub2 to load properly at startup. Thank you, everyone for helping.