To expand on this: It was also a pretty contentious issue. The canon was not “self-evident” but required plenty of consideration over an approximately 300 year period after the last book was written, provided we use the Council of Carthage in 397 as the standard for when it was established. It took the Church to establish a standard canon.
Of course, Protestants themselves put the difficulty back on display. Not only did they require us to re-declare (again) the canon from Carthage, they couldn’t even agree on a canon themselves for some time. Despite their love of St. Augustine, they rejected his version of the canon. Luther made changes to both the Old and New Testament, and most Protestants today don’t accept his canon. Calvin, if I remember correctly, still wanted to keep a Deuterocanonical book (I think Baruch) to stay consistent with his use of St. Jerome to establish his canon.* Obviously, Protestants ended up rejecting that as well.
*Edit: It is somewhat debatable how far his respect for Baruch went. Calvin, in general, had some degree of respect for the Deuterocanonical books, certainly more than your average modern-day Protestant. He did not, however, include Baruch in his list of of books to reject as of equal importance to other books, and his citations from Baruch seem to indicate that he saw it as Scriptural.