Grub menu does not show up?
Can you boot now into manjaro?
How, if the boot menu does not show?
Above quotes shows it did.
Please confirm. Can you boot into manjaro?
ps: don't worry about tmpfs now. It doesn't matter. And it doesn't matter if it is in fstab or not in fstab. We don't need to worry about it now.
ps: there is no need to reinstall Arcolinux.
Just change the fstab uuid for its /boot/efi
Then from Manjaro grub (if it is working, it should be) manually boot Arco and then just do grub-install && update-grub.
To boot manually arco, at manjaro grub menus, go to prompt and boot manually
grub> set root=(hd0,3) # if it is in sda3, if sda4, (hd0,4)
grub> linux /boot/vmlinuz-linuz root=/dev/sda3 rw
grub> initrd /boot/initramfs-linux.img