This is my situation:

I have a laptop with UEFI, Secure Boot can't be turned off at all.
There are 2 ssd drives: the first one with Windows 10 and the second used to be a storage drive in NTFS.

I've shrinked the partition of the second drive from Win10 to make room for Ubuntu. So there was unlocated space at the end of the drive.

I've phisically removed the Win10 ssd drive from the laptop because I don't want to risk touching it at all.

I've launched Ubuntu 19.04 from a USB pen (created with Rufus). I had to use nouveau.modeset=0 at boot otherwise Ubuntu would freeze (nvidia 1070 and intel integrated gpu).

I've created in the free space from Ubuntu 3 partitions: an EFi of 1 GB, a root and a home partition in extfs4.

The installation starts but it gives me a fatal error while installing GRUB and that's it.

I've also tried to get back into live Ubuntu and reinstalling GRUB from there (mounting the EFI partition in a temp dir). The intallation looks fine but alas, the machine can't find anything to boot when I reboot it.

What's going on?