I have an EKS cluster and today my subnet had
0 Available IPv4 addresses.
Does that mean that there are limits per nodes within 1 cluster in EKS?
You should read the official EKS documentation for this. But based upon your question, your subnet having 0 Available IPs means that your cluster depending on how many nodes it has, cannot provide more IPv4 for Pods(for example). It all comes down to the size of the cluster, as each Node size comes with its own IPv4/6 limits. You can check that here.