Optional options in a Custom Node

Hello!
I am in the process of building a custom node but I have some issues dealing with optional options.
I am using declarative style and the node is basically helping the user composing a url to fetch some data.

I need to let the user add multiple query parameters from a predefined list.

I am at the point where the user select the operation that he wants and then I would like te node to show the button to add additional query options to add to the url, but currently I don’t know how to do that. I can make them appear all at once but, as I said, I want the user to pick them up from a list and hide the other ones.

How to do that?

Thanks for the help.