Of cause there are multiple ways to set this up and there are definitely more details than would fit into one post. One possible quick-n-dirty approach:
take a new unused switch (or use VLANs)
connect one NIC on each PVE node here
connect the NFS server here
configure a new bridge with that new NIC on each node. (Using the NIC w/o a bridge is absolutely possible, but this opens more future use cases.)