I don’t follow the logic here. Fr. Barron says very clearly that the story is theologically true. Original sin is a theological claim. You don’t actually show how Fr. Barron’s statement poses a problem for original sin. (And the fact that Richard Dawkins thinks it does is not, in my opinion, a point in your favor

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You seem to be assuming that “myth” is something trivial or unreal.
The apparent contradiction with Humani Generis is something I wish Fr. Barron would speak to. The infallibility of papal encyclicals, if I’m not mistaken, can’t simply be taken for granted. It seems pretty clear to me that papal encyclicals in the past have sometimes said things that turned out to be wrong, or condemned propositions that turned out to be true. I recognize that many folks on this forum put a lot of effort into showing that this isn’t the case (see rinnie’s recent thread on Exsurge Domine and the burning of heretics, for instance), but even if these efforts are valid, a similar effort could probably bring Fr. Barron’s statement into line with Humani Generis.
Still, in the absence of clear indications that the Church is willing to back away from some of what Pius XII said in Humani Generis, and in the absence of an explanation showing how Fr. Barron’s statement agrees with HG, I can see why folks would be reluctant to follow Fr. Barron on this point.
Edwin