This question displays an incomplete understanding of how the boot process works. In such a system, /boot (ext4) and /boot/efi (FAT) are unencrypted. Once the kernel and initrd are loaded, your root filesystem can be whatever you want: LUKS, btrfs, ZFS, XFS, LVM, anything.
How does removing GRUB_ENABLE_CRYPTODISK / LUKS improve security?