OPML is the standard formatting for exporting subscriptions. Your subscriptions OPML are online at https://player.fm/˂your username˃/subs.opml (make sure you're logged in or your subscriptions are set to public).
You can also receive a "live" feed of your subscriptions at use https://player.fm/˂your username˃/subs.rss. This is useful if you want to access your Player FM subscriptions from another podcast app (e.g. on a platform where Player FM doesn't have a native app). By subscribing to this URL in the other app, it will stay up to date with the latest episodes and any subscription changes you make in the future.