dcc.Upload - backend part in Heroku?

I have been researching about uploading data (by external users) to my app and it seems the only way indeed is the dcc.Upload component… To clarify it is this uploaded file that will be read into pandas and fed into the callbacks for analysis and visualisation (plotting).

However, I also read about Heroku simple-file-upload config (Simple File Upload | Heroku Dev Center) and the AWS S3 bucket (Using AWS S3 to Store Static Assets and File Uploads | Heroku Dev Center) as the necessary way to store static data uploaded to the app (like images and data files). Nowhere is it mentioned in the Dash dcc.Upload docs about the storage of the uploaded file, i.e. the web server part and the UI are not linked together in any documentation I could find.

Can anyone explain to a total web dev newbie, once deployed to Heroku, does the dcc.Upload require the set up of the Heroku simple-file-upload feature config or an S3 storage bucket ? If not, how does it deal with the storage of the file?

PS I am not even sure the data file the user will upload is a ‘static’ file or a dynamic one, as it will obviously be processed within the code for the analysis to happen (ie group, sort, filter, etc)