The Codex Sinaiticus (Shelfmark: London, British Library, Add MS 43725), designated by siglum א [Aleph] or 01 (in the Gregory-Aland numbering of New Testament manuscripts), δ 2 (in the von Soden numbering of New Testament manuscripts), or Sinai Bible is a fourth century Christian manuscript of a Greek Bible, containing the majority of the Greek Old Testament, including the Apocrypha along with the deuterocanonical books, and the Greek New Testament, with both the Epistle of Barnabas and the Shepherd of Hermas included. It is written in uncial letters on parchment. It is one of the four great uncial codices (these being manuscripts which originally contained the whole of both the Old and New Testaments). Along with Codex Alexandrinus and Codex Vaticanus, it is one of the earliest and most complete manuscripts of the Bible, and contains the oldest complete copy of the New Testament.[1] It is a historical treasure,[2] and using the study of comparative writing styles (palaeography), it has been dated to the mid-fourth century.
https://en.wikipedia.org/wiki/Codex_Sinaiticus
In other words, it is from about 350 AD. It was kept in a Greek Orthodox monastery. It dates from before the origin of the Catholic church in the Great Schism of 1054.
You’ve got it backwards.
The Catholic Church predated the schismatic Orthodox church, which originated in the Great Schism of 1054.