hi. first of all thanks @pocopico for this great tool.
finally i managed to create a uefi bootable flash drive. the steps are very easy but it took me about the whole day to figure out.
after writing redpill tc loader image to your flash drive, you need a linux machine to add the uefi boot.
in my case, i have a notebook with linux mint installed (latest edge edition).
assuming that my flash drive was /dev/sdb, this is what i've done:
Mount the filesystem:
sudo mount -o umask=000 /dev/sdb1 /mnt
Write the MBR and install the grub files required for legacy BIOS boot on the drive: (i don't know if this step is really needed but anyway it works)
sudo grub-install --no-floppy --boot-directory=/mnt/boot --target=i386-pc /dev/sdb
Install /EFI/BOOT/BOOTX64.EFI and other grub files required to load grub from a 64-bit UEFI firmware:
sudo grub-install --removable --boot-directory=/mnt/boot --efi-directory=/mnt --target=x86_64-efi /dev/sdb
Unmount the filesystem:
sudo umount /dev/sdb1
after that, remove the flash drive and try it. for me, it worked at first try. no need to edit any other file.
credits go to https://github.com/ndeineko/grub2-bios-uefi-usb for this helpful page without which I would never have succeeded.