Overcast’s Upload Files function was removed with the most recent update to iOS 13, I think; the option is disabled in its settings and the uploads page is gone from the website. I could not find any info about this change online. What annoyed me was that this capability was removed while I was in the middle of listening to an uploaded audiobook file.
So am reluctantly moving my podcast listening to Castro, which has most of the functionality I use plus lets me add audio files more easily.
I will miss the custom playlists feature of Overcast; I divvy all my Sleep With Me and ambient music podcasts into their own playlists, for example.
I was so comfortable in my technological rut! But am making the best of it. I’ve stopped most all the feeds in Overcast and am starting fresh in Castro. I have a huge backlog of audiofiles in Overcast anyway, so maybe I can whittle them down while keeping up with my current diet of audio snack foods.