A subscription export should be easy to open in another podcast app. OPML is a common outline format for this job, but its usefulness depends on the entries your application writes.
A title-only list may be readable to a person while giving another app too little information to find the feed. Use the format and fields expected by the documented export path.
Export the listener's actual choices
Build the request from the authenticated account. Include follows rather than every catalog item the person has ever viewed. Keep private app notes or listening history out of a subscription file unless a separate, clearly described format includes them.
Use current feed addresses where the catalog provides them. Preserve a meaningful title as display context. Escape XML characters correctly so a show name containing an ampersand does not break the document.
If you retain folder organization, check how your chosen format and target apps handle nested outlines. Do not promise perfect preservation across all applications without testing those cases.
Try the file somewhere else
Export a controlled account with several shows, including a non-English title and punctuation. Parse the result with an independent XML reader and import it into a test destination that supports OPML.
Also export an account with no follows. The file should remain valid and the interface should explain that the list is empty.
Avoid exposing the file at a predictable public address. Even a list of public feeds can reveal a person's interests. Deliver it through an authenticated download or another reviewed path.
Podnivo documents subscription portability, while your app owns the button, account checks, and download experience that make the export useful to a listener.