At first: I notice you think in concepts of forms. Within Mendix we talk about pages. And pages != forms in the technical sense.
Mendix uses objects in their pages to do something with data. Which could be show the data, manipulate the date, trigger some app logic etc.
A form can be seen as a interface with data, which is decoupled from the database.
Within Mendix objects are the link between your database and your front end (pages) in pages you are still dealing with objects. not with data in JSON/XML format which you need to map to objects (server) and records (database) .... please note Mendix also uses JSON in their server client communication. But is not what you do yourself and consider when modeling. Objects are the concept.
So why above? Because depending on your Business needs I can answer your question differently, making use of above.
Two scenarios I can think of:
For the first scenario you want to search and use. In that case I would not start with a pop up showing all. I would search through a list in a page using filter widgets.
If the requested UI is the way to go; I would do it las follows
For the second the same as above, but when object found
Done