This is caused because the user is running as qemu for virt-resize and if qemu does not have privileges to read from the source and write to the destination, it will fail with the below. So either change the uid of qemu or change the ownership of the source and target.
virt-resize --expand /dev/sda2 /root/kvmtemplates/windows2019-eval-template.img /root/kvmguests/kvmkvmuser4515........
This is useful if you are installing Windows and need virtio but of course Windows needs the virtio driver which is on a second iso.
This is the line of code you would add to your kvm startup script and then you get this iso as second cdrom you can browse to for your Windows install of virtio driver's or whatever other use you need it for.