I am using the summary control, and I am trying to figure out if there’s a way that I can hide the fields which are blank or not selected by the user, rather than keeping them empty.
I am not sure what you mean by fields. There is a simple logic to get to know if a control is empty or not.
Use ISEMPTY() name of the control inside. It will return TRUE if it is empty. And False otherwise.
Assign the output of this function to a toggle control.
You can set a rule, show and and hide control depending on true or false value of that toggle.