How do I prevent node enumeration?
This is difficult, because it is core functionality.
What you could do to prevent people from checking node/4, node/5 etc is blocking access when a url request has a certain structure. You'd need a custom module with an EventSubscriber.
Here is an example how to intercept such url requests and how to redirect them. In this case it is a taxonomy term view but the underlying thought is the same: https://stefvanlooveren.me/blog/redirect-taxonomy-terms-filtered-view-page
Further, you'd have to check in your html rendering that every reference to a node id is hidden. Quite some work but if it is really necessary its possible.