Most podcast apps allow you to export your subscriptions in OPML. Overcast supports this plus an "extended" format which also contains every podcast episode you have downloaded. You can get your personal version on the Overcast account page.
Here's an example of what you'd find in that file:
<!-- Just an example, this isn't the whole file -->
<outline type="rss" overcastId="323006" text="Cortex" title="Cortex"
xmlUrl="https://www.relay.fm/cortex/feed" htmlUrl="https://www.relay.fm/cortex" subscribed="1">
<!-- I listened to this whole episode -->
<outline type="podcast-episode" overcastId="346825202660328"
pubDate="2020-12-14T07:45:00-05:00" title="110: 2021 Yearly Themes"
url="http://relay.fm/cortex/110" overcastUrl="https://overcast.fm/+E7b4kA8-g"
enclosureUrl="https://www.podtrac.com/pts/redirect.mp3/traffic.libsyn.com/secure/cortex/Cortex_110.mp3"
userUpdatedDate="2020-12-14T15:08:20-05:00" userDeleted="1" played="1"/>
<!-- I only listened to part of this episode -->
<outline type="podcast-episode" overcastId="346825866223649"
pubDate="2018-09-19T08:45:00-04:00" title="74: The Biggest Challenge of Being a Human"
url="http://relay.fm/cortex/74" overcastUrl="https://overcast.fm/+E7b7COICE"
enclosureUrl="https://www.podtrac.com/pts/redirect.mp3/traffic.libsyn.com/cortex/Cortex_074.mp3"
userUpdatedDate="2020-12-02T14:22:13-05:00" userDeleted="1" progress="5968"/>I wanted to get this data and put it in a more readable place so I made a Shortcut. Download it here. This one just parses the podcast info from the OPML. This should be a good starting point if you wanted to do something with the OPML data.
As an example, I made a separate Shortcut which moves all the OPML data into my app, Podmark. Get that Shortcut here.