I am clean installing 18.04 to a partition. All went smoothly until this error. "The 'grub-efi-amd64-signed' package failed to install into /target/. Without the GRUB boot loader, the installed system will not boot". After pressing 'ok' the following opened. "Installer crashed" "We,re sorry the installer crashed. After you close this window, we'll allow you to file a bug report using the integrated bug reporting tool. This will gather information about your system and your installation process. The details will be sent to our bug tracker and a developer will attend to the problem as soon as possible" Has anybody had the same issue and had a resolution.
"package failed to install into /target/" indicates the installer program can't locate the partition as assigned and/or format is not correct. If installing using UEFI BIOS then you must have an /EFI partition which is created as GPT not MBR. Once this is successful, you can usually proceed without issue.
However, if your system is older like mine, and it doesn't have NVME drive boot options but you can "see" the drive in setup, then the installer will not be able to locate the NVME drive for boot files and GRUB loader. In this case, you may be able to use an HDD or SSD to install the /EFI partition and use it to install GRUB and boot from there to the NVME drive.
Note the size of the /EFI partition should be about 100 megs if dual booting. If you need to install several OS's all on the same drive then you might need to increase the size of the /EFI. On my system with Kubuntu and Windows 10, my boot files have used only 30 megs of the 100 meg partition.
I had this when I installed using manual partitioning with root, /swap and /home partitions.
I succeeded when I also created an EFI partition (500MB at the start of the disk), following advice gleaned from this tutorial