When doing an iso restore, I noticed that it was not booting correctly through UEFI (including when I actually tested it), but I solved the problem manually, which may help you a bit
Create UFI partition : fdisk /dev/sdb (n 1 enter +512M t [EFI System] w)
https://github.com/nerun/remastersys/blob/458fcbb41c4cd4f405385f435332207725c6c8a4/remastersys/usr/bin/remastersys-installer#L110
When doing an iso restore, I noticed that it was not booting correctly through UEFI (including when I actually tested it), but I solved the problem manually, which may help you a bit
fdisk /dev/sdb
(n 1 enter +512M t [EFI System] w)sudo apt-get install dosfstools
sudo mkfs.fat -F32 /dev/sdb1
sudo mount /dev/sdb1 /boot/efi
sudo grub-install /dev/sdb --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=GRUB
echo "/dev/sdb1 /boot/efi vfat defaults 0 1" | sudo tee -a /etc/fstab
DELL BIOS Examples