Martin Luther nailed his theses in 1517. Somewhere between 850 and 1200, the Roman Catholics and the Orthodox churches had split. The traditional date is 1054, and by 1190 we have this statement from Theodore Balsamon, Patriarch of Antioch:
“For many years [he does not say how many] the western Church has been divided in spiritual communion from the other four Patriarchates and has become alien to the Orthodox … So no Latin should be given communion unless he first declares that he will abstain from the doctrines and customs that separate him from us, and that he will be subject to the Canons of the Church, in union with the Orthodox.”
orthodoxinfo.com/general/greatschism.aspx
So there were at least two different bodies claiming to be Christian churches long before Luther came around.
One of the reasons the word “Catholic” with a capital C is confusing is because at least three distinct groups refer to themselves as “catholic”: the Orthodox Christians, the Roman Catholics, and the Anglicans. As mentioned before, the Orthodox have always used the Septuagint, which was in place long before Christ was born, so the Catholic Church did not determine the Old Testament. The earliest record existing that lists the 27 books of the New Testament is an annual Easter letter written by Athanasius, Bishop of Alexandria, in 367. The church at Rome was a bit behind the East in formally recognizing the 27 NT books:
“The West began to realize that the ancient Apostolic Churches of Jerusalem and Antioch, indeed the whole Orient, for more than two centuries had acknowledged Hebrews and James as inspired writings of Apostles, while the venerable Alexandrian Church, supported by the prestige of Athanasius, and the powerful Patriarchate of Constantinople, with the scholarship of Eusebius behind its judgment, had canonized all the disputed Epistles. St. Jerome, a rising light in the Church, though but a simple priest, was summoned by Pope Damasus from the East, where he was pursuing sacred lore, to assist at an eclectic, but not ecumenical, synod at Rome in the year 382. . . The Damasan catalogue presents the complete and perfect Canon which has been that of the Church Universal ever since.”
newadvent.org/cathen/03274a.htm
So yes, the church decided which books were to be included in the New Testament, but to say that it was decided by the Catholic Church, if by that you mean the Roman Catholic Church, is not supported by history.