Thanks. My podcast is hosted with Libsyn, and the response from Libsyn Support is that they do not provide or support MRSS feeds.
I don't have any previous version of any Roku channel. All I have at this point is an audio podcast. I want to convert that to a video format and create a Roku channel for it. In following the steps at https://blog.roku.com/developer/tutorial-podcasts, the very first step is to find my MRSS feed URL. But the "simple feed finder" they included is no longer there. That's where I've hit a dead end so far. I've run a computer business for 20 years, but this stuff is a new area for me.