I remember the Catechism (someone should provide exact citation) teaching that the Old Testament for Catholics is to be interpreted only as a tool to understand the New Testament properly. Historical data and creation narrative from OT is relevant for us only in so far as it is a background for the Incarnation and Resurrection, with the latter being the only true Creation.
**CCC 129 ***Christians therefore read the Old Testament in the light of Christ crucified and risen. Such typological reading discloses the inexhaustible content of the Old Testament; but it must not make us forget that the Old Testament retains its own intrinsic value as Revelation reaffirmed by our Lord himself. Besides, the New Testament has to be read in the light of the Old. Early Christian catechesis made constant use of the Old Testament. As an old saying put it, the New Testament lies hidden in the Old and the Old Testament is unveiled in the New.
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Yes we must use to the Old Testament to interpret the New, but we also must use the New Testament to view the meaning of the Old. We cannot simply dismiss the OT as background information because it holds the same Divine Revelation that the NT does and its message must be given its due.
As for the OT being mythical and being grossly historically inaccurate, this view (I believe) mainly comes from scholarly pride and does not coincide with Catholic Dogma. Generally, I have found, when someone purports this theory, they do so based upon the assumption that everything we currently view as historical fact is true.
I will give you an example where the scholars were proven wrong and the OT proven correct. Before 1822, scholars of “Biblical Archaeology” were certain that there was never a Philistine people that the Israelites came into conflict with as depicted in the OT. They thought this because the actual word ‘Philistine’ was never used during the time there were depicted in the OT. In 1822, however, by examining inscriptions discovered in Egypt they found that they actually did exist, but it was just under a different name, known in Egyptian as the Peleset. It seemed that over the course of history, the Israelite scribes had translated the original Peleset name into Philistine because that was the contemporary Israeli name for the Peleset people.
The modern dismissal of Exodus can be ultimately summed up as “We currently have no evidence that affirms that Exodus happened, so, therefore, the account is simply a fictitious account.”
Personally, I trust the Holy Spirit enough not to let such horrendous falsehoods exist within Scripture that is intended to he historical.