Podcasts are normally plain mp3 (or similar) files that get downloaded as-is off an rss feed, as far as I understand. I don’t think anyone gets extra ads outside the sponsored/host-read ones.
The big podcast networks like iHeart are able to dynamically splice ads into episodes, so they can be targeted based on geoIP or whatever other signals they have on you.
Everyone posts to centralized RSS feeds these days. The company that owns the feed creates duplicates of the uploaded file, inserts ads into them, and serves a version of the file containing ads localized to the downloader's country.
If the same podcast is uploaded to Youtube through the uploader's official channel, it won't contain those ads and you're better off downloading that.
