I recently performed a dual-boot installation of Manjaro and I have encrypted my root partition. When I boot, I am asked to enter the passphrase for this partition before I reach the Grub. If possible, I want to change this, so that the passphrase is requested after selecting to boot into Manjaro (not Windows).
During installation, I specified the existing boot partition with 512MB to have a mount point of /boot/efi, and if I recall correctly I flagged this as boot.
first know whether the machine is booted with UEFI or with Bios - I assume it is UEFI
then you need not only a /boot partition
but an EFI system partition as well - this has to be a FAT filesystem and of Type ESP
and be mounted to /boot/efi
Mount your unencrypted soon to be /boot partition somewhere
mount the EFI partition to it
then copy the contents of your current /boot to that location
Then adjust /etc/fstab - so that the unencrypted /boot and /boot/efi is mounted
You will probably need to boot the live system, chroot and re-install grub afterwards.
It is all a bit confusing - it certainly was for me.
I did it the other way around.
I first installed normally, unencrypted.
Then I later moved everything but /boot to an encrypted partition I had also created.
Then I got rid of the original unencrypted partition and grew the encrypted partition to use all the space.
This above is the result of that procedure.