Welcome to the forum! 
Um, mhwd doesn’t need to be downloaded, as it’s already on the live medium. And yes, /boot is not an EFI partition, because that’s not where the EFI partition would be mounted. The EFI system partition has to be mounted at /boot/efi ─ at least, if you’re using GRUB as the boot loader.
But okay, I’ll try talking you through it, albeit that I have no experience with NVMe drives. 
Boot up from the live medium and start the partition manager ─ it’s in the menu somewhere ─ and recreate the partition where the old one used to be. It should be about 512 MiB in size, but if the available space is smaller, then just use that space.
The partition should also be formatted with vfat (FAT32), its mount point should be set to /boot/efi, and it should have the boot and esp flags set. Don’t worry if the partitioning tool won’t let you set an esp flag ─ it may do that automatically, depending on which partitioning tool you use.
Important is to write down both the partition identifier ─ I am guessing it’ll be /dev/nvme0n1p1, but it may also have a different number as the last character ─ as well as the UUID for the formatted partition.
After doing the above, open up a terminal window and issue… 
su -
… to become root within the terminal session. Now, assuming that your EFI system partition is /dev/nvme0n1p1 ─ change this is needed ─ issue the following commands…
manjaro-chroot -a
mount -t vfat /dev/nvme0n1p1 /boot/efi
grub-install --recheck --no-rs-codes --target="x86_64-efi" --modules="part_msdos part_gpt" --efi-directory="/boot/efi"
update-grub
nano /etc/fstab
Now make sure that you put the UUID for the new EFI system partition in place of the old one. Use Ctrl+O and Enter to save the file, and Ctrl+X to exit nano.
If all went well, you can leave the chroot with…
exit
… and then it should be safe to reboot your system.
I see what you did there. 