Hello,
Your GPU has loaded radeon driver so I think you cannot bind vfio on it.
in the guide, have you followed this section ?
echo "options vfio-pci ids=10de:1381,10de:0fbc" > /etc/modprobe.d/vfio.conf
and blacklisted radeon driver ?
echo "blacklist radeon" >> /etc/modprobe.d/blacklist.conf...