Run this script using su instead of sudo. The ">" redirects of echo will not work otherwise.
Add this to grub, /etc/default/grub:
intel_iommu=on (or) amd_iommu=on
rd.driver.pre=vfio-pci
kvm.ignore_msrs=1
Add this to /etc/mkinitcpio.conf:
MODULES="vfio_pci vfio vfio_iommu_type1 vfio_virqfd"
FILES="/usr/bin/vfio-pci-override.sh"
Hooks="... vfio ...."
This guide is based on:
https://wiki.archlinux.org/index.php/PCI_passthrough_via_OVMF#Using_identical_guest_and_host_GPUs and https://forum.manjaro.org/t/virt-manager-fails-to-detect-ovmf-uefi-firmware/110072