I don’t know when this started but I noticed it for the first time a few months ago. Some podcasts will have preroll ads that are obviously tailored to me since they are not in the same language as the podcast, instead they are in my native language and if I connect to a VPN in another country the ad will change to one from that country. They also seem to appear regardless of podcast app. I have used both AntennaPod and Spotify. AntennaPod is free so I guess they source their podcasts from some third party website that could be adding in the ads. But since I am paying for Spotify I am expecting not to have to listen to any ads. So who is adding in these ads? Can I get rid of them or am I just stuck with them?
Podcasts partner up with ad providers. They inject ads into the episodes depending on several factors, including your location. The podcast has some say and can for example exclude some topics like politics. That catches most, but an ad can also be misrepresented and slip through.
I use Antennapod as well and they have nothing to do with it. They just download episodes from RSS feeds provided from other services.
You could use a VPN server in a smaller country. If the ad market is very small, there simply might be no ads to serve you.
I can also recommend using a swiss VPN server. The funny swiss dialect makes it hilarious.