The AppData folder in your package will appear under the VFS folder under the package root, just like all other VFS folders. Except that without the PSF FileRedirectionFixup, your app is unlikely to see the files. Explanation:
Software running in the container (without PSF) generally maps native file requests to also check the appropriate VFS folders under your package root. Unfortunately, it doesn't map requests to the local AppData or LocalAppData folders to the VFS folders. We don't know why, it just is that way.
Adding in the FileRedirectionFixup of the PSF can make these folders visible, as well as making them modifiable. When one of those files is referenced, it would be copied out to the user's AppData/Local/Packages/[PackageName]\LocalCache\Microsoft\WritablePackageRoot\VFS AppData folder and opened from there.