Yes, but you’d need to install grub without installing Manjaro (manual grub install) and then copy one (or more) ISO file(s) to an external storage medium (HDD, SSD, SLC USB stick,…), because 64GB is not a lot and that’s more of an expert thing to do.
This is the Manjaro forum and we’re very good at deleting Windows, but we’re not very good at keeping it in the air, so you should take that question where it’s on-topic.
