The OpenSwim is great but managing podcasts on it is genuinely annoying, you have to manually drag files, figure out the right folder, sort out the order yourself. I felt this was so annoying that I basically stopped using them. A friend of mine had the same issue and built an app called Pod2Swim that fixes this.
The app makes this way more convenient. You subscribe to any podcast, queue up episodes, and export them to the headset in one tap, in the right playback order. No phone at the poolside, no streaming needed.
It’s called Pod2Swim and it’s on the App Store if anyone wants to try it: https://apps.apple.com/us/app/pod2swim/id6766092966
Give it a look - and if something doesn’t work the way you’d expect, reach out to him directly. He’s actively working on it.