This topic: https://docs.openshift.com/container-platform/4.17/virt/post_installation_configuration/virt-post-install-network-config.html#virt-selecting-migration-network-ui_virt-post-install-network-config

Is missing the following prereq:

Prerequisites
You created a network attachment definition for the network.

While fixing this, we should also review the following sections to determine if that prereq is missing for other web console procedures:
Virtualization > Postinstallation configuration > Network configuration
Virtualization > Networking