Hello there,
All questions are good questions I say 🙂
So, the Instantiate node is a Function node. By default, Function nodes do not have Flow Input/Output Ports, but there is an option in the node inspector named “Callable”. By enabling this option, you will get 1 Input and 1 Output Flow Ports like you desire and thus possible to become part of the flow 🙂
You can read more about Function nodes here if you like: