While I am not a chr*stian, it is quite maddening that the “unchanging” Catholic Church used to believe the “first Adam” was a real as the “second Adam,” but now the “first Adam” was merely a literary form.
This is untrue. The Church teaches that Adam did exist and all sin stems from him.
CCC:
374 The first man was not only created good, but was also established in friendship with his Creator and in harmony with himself and with the creation around him, in a state that would be surpassed only by the glory of the new creation in Christ.
375 The Church, interpreting the symbolism of biblical language in an authentic way, in the light of the New Testament and Tradition, teaches that our first parents, Adam and Eve, were constituted in an original "state of holiness and justice". 250 This grace of original holiness was "to share in. . .divine life". 251
The Church teaches no such thing. Quite the contrary, the view you falsely ascribe to the Catholic Church is expressly condemned. It is blatant heresy, even if you happen to have heard it from Father Flake or Sister Silly.
Humani Generis His Holiness Pope Pius XII Encyclical Letter Concerning Some False Opinions Which Threaten to Undermine the Foundations of Catholic Doctrine August 12, 1950
37. When, however, there is question of another conjectural opinion, namely polygenism, the children of the Church by no means enjoy such liberty. For the faithful cannot embrace that opinion which maintains that either after Adam there existed on this earth true men who did not take their origin through natural generation from him as from the first parent of all, or that Adam represents a certain number of first parents. Now it is no no way apparent how such an opinion can be reconciled with that which the sources of revealed truth and the documents of the Teaching Authority of the Church propose with regard to original sin, which proceeds from a sin actually committed by an individual Adam and which, through generation, is passed on to all and is in everyone as his own.[18] >37. When, however, there is question of another conjectural opinion, namely polygenism, the children of the Church by no means enjoy such liberty. For the faithful cannot embrace that opinion which maintains that either after Adam there existed on this earth true men who did not take their origin through natural generation from him as from the first parent of all, or that Adam represents a certain number of first parents. Now it is no no way apparent how such an opinion can be reconciled with that which the sources of revealed truth and the documents of the Teaching Authority of the Church propose with regard to original sin, which proceeds from a sin actually committed by an individual Adam and which, through generation, is passed on to all and is in everyone as his own.[18]
That's completely false and you bear false witness when you repeat it.