This article is an example of a Catholic Apologetic argument against the truthfulness of Sola Scriptura (abbreviated SS).
It sets up a logic trap:
Assume SS is true
SS asserts itself to be more important than all church tradition
SS is not in the Bible (otherwise Protestants could point to it)
SS is not logically derivable from truths in the Bible
Therefore SS is an extra-Biblical doctrine
SS denies that any extra-Biblical doctrines are essential for salvation
SS is not essential for salvation
Therefore SS is not true
I have a few problems with the logic.
A) Does SS assert that it is necessary for salvation?
B) Does SS assert that all useful truths of God are either in the Bible or deducible from it?
According to Gödel's incompleteness theorems, in any sufficiently complex mathematical system whose axioms are consistent, there are undecidable propositions. That is, one can phrase statements in that system that are true (or false) that can neither be proven nor disproven.
This leaves us with the situation that God may reveal to both Protestants and Catholics ideas that are true and useful yet are neither contained in Scripture nor essential for salvation. Thus it is possible that belief in SS is true and useful but not required.
Why would God leave out such a truth with such significant ramifications for the historical development of the church?
Scripture has numerous places where people are told that answers to certain questions would not be given to mankind.
Jesus said that the time of his return was known only to the Father. That is a pretty significant piece of information! Many people, falsely believing that Christ was about to return, have done foolish things.
John was told to seal up what the seven thunders said (in Revelation).
Daniel was told to seal up some of his prophecies until the time of the end. I assume that means to encrypt them by using figurative language or altering the order of some events.
It is clear that the Catholic Church and the Protestant Churches are on different trajectories. One can be right and the other wrong. Both can be partly wrong about things. What is certain is that God has different roles for each church to play.
It reminds me of the change in computer chip architectures a few decades ago. For years, each chip had more instructions than the last. This had advantages and disadvantages. Some researchers decided to buck the trend and create chips with fewer insructions (RISC: Reduced Instruction Set Chip), hoping that they would be able to design them faster, make them execute faster, more reliable and better combine them into parallel architectures. Maybe the Protestant Church is a RISC God decided to take? Fewer traditions, easier to change direction during rapidly changing times. Not necessarily having more truths or better truths, just more maneuverable.
In the physical world, there are basic laws and lots of stuff. The laws we can't change, but within them, by our creativity we can create many marvelous things from that stuff. Those things aren't necessary, but they are useful. God is creative in building His church. God is beyond necessity. He can create things just for the joy of making things. He did it with all the species of animals; he does it with beasts (kingdoms: Job 40 and 41, God delights in Behemoth and Leviathan). Why not the church, too?