Spice (server) was deprecated in RHEL8.3 and completely removed in RHEL9.
For customers upgrading the RHEL KVM hosts from RHEL8 to RHEL9, they should first switch all existing VMs from SPICE to VNC before the upgrade, as preparation steps. However, if they do not, the VMs will fail to start on 9: https://access.redhat.com/solutions/6955095

From here, the situation is tricky for the customer. Due to domain validation, an XML with qxl/spice elements will fail to validate. So the only way out is a manual, all-in-one edit of the XML, switching from VNC to SPICE.

Unless I am missing something, this is not a simple task from the command line. Please implement a way for the user to configure the graphics of the VM easily via virsh, so the user is able to switch from SPICE to VNC and start the VMs.