Then I won't rely on any graphical grub installer.
The UEFI-installation in a terminal is already described here
https://forum.kaosx.us/d/1572-installing-grub
I know from another topic that you use btrfs as root filesystem. Be aware, that the grub binaries should be placed on a separate subvolume to prevent them from fragmentation through COW (Copy-on-Write), if you use snapshots and rollback to snapshots. They must stay aligned and contiguos.