Focusing on the work of Ecumenism, the DVP hosts consider the issue of "Communicatio in Sacris," that is, the act of a Catholic taking part in the worship of non-Catholic Christians, particularly Protestants. The main question to consider: Is it possible for a Catholic to attend Protestant worship services and only participate passively?
Here are the articles relevant to the episode.
Catholic Answers: https://www.catholic.com/qa/are-catholics-required-to-attend-non-catholic-services-instead-of-mass-for-the-sake-of-ecumenism
The Fr. Thomas Crean O.P. article: http://www.christendom-awake.org/pages/thomas-crean/praying-with-non-catholics.htm
Further Reading:
https://onepeterfive.com/worship-non-catholics/
https://www.vatican.va/archive/hist_councils/ii_vatican_council/documents/vat-ii_decree_19641121_unitatis-redintegratio_en.html