The file is a backup of data from the app.
It is clear to me that I do not need the extension saf for this.
However, should the user delete and reinstall the app or reset (erase) the app's data, they can use the backup to feed their app back up with the backed-up data.
I am currently creating a folder under Download and backing up the data there. From there, after selecting the file, they can be copied to the ASD using saf and then restored.
I am aware that storing in the cloud is the safest way to back up the data. This is particularly important if the app is to be reinstalled on a new phone. With my current solution, the user has to save the file himself when changing smartphones.
I've already experimented with the linked information.
Since my backup file can quickly become 100 to 200 MB in size, this doesn't seem to work.
On a smartphone, it's better to backup the data in batches (directly to the Cloud), at the time it is created - so ten or twenty files of 10mb each during the course of one session, or, depending how the data is created, temporarily stream to a file in the ASD first, then upload that to the Cloud (again, strictly monitoring file size). We don't know what your App actually does so it's difficult to give more specific help.