Create backup file in external storage

backupfile.kt

fun onLocalBackupRequested(activity: Activity) {
    val mimeTypes = arrayOf("application/zip")
    val fn = getBackupFileName(prefix)
    val intent = Intent(Intent.ACTION_CREATE_DOCUMENT)
        .addCategory(Intent.CATEGORY_OPENABLE)
        .setType("application/zip")
        .putExtra(Intent.EXTRA_MIME_TYPES, mimeTypes)
        .putExtra(
            Intent.EXTRA_TITLE, fn
        )
    activity.startActivityForResult(intent, 695)
}