Depending on, if you are expanding your infrastructure, or only want to use the perpetual licences.
If you are on the way of perpetual licence is enough in capacity (CPU sockets), then you can continue using them without purchasing anything else.
If you are expanding the cluster, then you need to purchase VVF for the new hosts and equal vSAN capacity for extension. - Not for the existing hosts.
If expanding the existing perpetual cluster, see the document about usage rights, second page:
https://ftpdocs.broadcom.com/cadocs/0/contentimages/VMware-vSAN-SPD-May2024.pdf