[ubuntu_mate] Cloned drive does not boot

So to be clear: sdb (another 1TB disk) is just a data drive?

Can you choose a boot menu at boot time? Not sure how to do it on a Lenovo; on a Dell or Acer, for example, generally you can hit the F12 key to get a boot menu and choose what device to boot from. If you can get a boot menu, what happens? Do you even see your disk as an option to boot from? I recently moved my Ubuntu + Windows SSD from one Acer laptop to another. I had to use efibootmgr to create a firmware entry on the new laptop for my SSD - otherwise, there was no option to boot from it. Boot repair could not fix my scenario but I think is supposed to fix stuff like that.

FYI, you don't have a boot partition now. You have an EFI partition (would be mounted in /boot/efi in Ubuntu). Are you saying you had a separate /boot partition (not EFI) on your old disk but not your new one? Or you meant you wanted to get rid of the EFI partition (which you were calling a boot partition)?

It seems you can convert to "legacy" (BIOS) mode from EFI but I've never done it. Try this:

https://help.ubuntu.com/community/UE...to_Legacy_mode

but that assumes in your Lenovo BIOS you an option to disable secure boot and switch to "Legacy" mode. Follow the instructions above to create a small /boot partition then run the boot repair as described - and hope it works!