In Files app, is the folder "on my device" created by app itself?

I know that in Files app I cannot create a folder "on my device" myself, so is the folder created app itself? In other words, if the app's developer doesn't support this feature, then I would have no way to create a folder for it?

I have only three folder now(not Apple's apps), and it is really inconvenient. For example, I store some ppts in Microsoft's PowerPoint app. It is saved "on iPad", but I cannot see them in Files.