That's because Podcasts *is* an AppKit app.
As also mentioned by someone else, actually no.
TV and Music are AppKit, but Podcast is actually a UIKit app with Catalyst.
I had a bug in beta 1, haven't upgraded to beta 2 yet so don't know if it's still there, where cmd+f would take focus to teach as expected, but the search field wouldn't work when activated like this - This bug was on TV and Music, and I wondered why not Podcast. Well, ironically the keyboard functionality was broken on the apps built natively for the Mac, not the app built for iOS and ported over.