The statement in our docs is not accurate.

If your cluster uses OpenShift SDN configured in either the multitenant or subnet isolation modes, you cannot migrate to the OVN-Kubernetes network plugin.

The migration can work with all SDN modes, but the functionality of multitenant mode cannot be preserved. For clusters run with the SDN mutlitenant mode, the cross project traffic isolation function will be dropped after the migration. Users have to configure network policies manually to achieve the mutlitenant isolation function.

This needs to be fixed in the documents of all releases.