Where are the dynamically generated files of an application deployed on Heroku stored?

Question

Heroku

Here, for sure, many people use heroku, so I also happened to have this question:
the application creates files that, when launched on localhost, were inserted into a certain directory, uploaded all this to heroku, the effect of the fact that the files are created is visible, information from them appears on the page, but I don't understand where these files are