As we know, the amount of services in a k8s cluster is limited. How do we break through the limit on the number of services when we use knative to develop serverless? What I can think of is to let knative support multiple clusters, how does knative support multiple clusters?
I think your suggestion in the comments is the correct one: you'll want to manage multiple Kubernetes clusters, and direct your individual users to different namespaces in different clusters.
I don't know of software to do this automatically, but you could use separate DNS records for each customer to point them to their cluster once the customer has registered.