I did my theological education after Vatican II, when Catholic enthusiasm for the Bible was at a peak probably never before matched in history. And I live in a historically Protestant country where Christianity consists of what is in the Bible. But I could never buy sola scriptura, the new-fangled belief of early modern North and Western Europeans that the Bible's text contained the knowledge of all things necessary to salvation and that its text was the ultimate regulator of Christian belief and practice.
And the more I read it and listened to it (for 20 years it was read out 3 times a day and every day for that time I joined in reciting or singing the Psalter) the less I could believe that it could ever serve that function.
In Greek, the dominant original language of Christianity, what we call "the Bible" is termed ta biblia...the books. I could never think of it as A book. In fact, it is a library. I wonder what effect would have been had on Christian history if somehow ta biblia would have found itself translated as The Library. Can you hear a new-born Baptist in Arkansas tell you, "Well, my Library says..."?
If ever there were a religion set up to believe in sola scriptura, it would be Islam. The Bible is an amalgam of the Hebrew scriptures with the 27 Christian scriptures added. Everyone knows that this library contains works by many different authors over a period of many centuries. But the Quran is the work of a single man, Muhammad. No "Old" Testament. A new book, spoken aloud by him and written down, so we are told, by others who heard him or who heard those who memorized what he said. All the material from the Hebrew or Christian scriptures comes in his own personal re-telling. (He understandably but erroneously thought that the Trinity was Father, Mother and Son.) Whatever I think of the content of the Quran, I have always admired the economy and simplicity of having one text totally replace all the others. No need for any other book. Or so you would think.
Even within the Quran, Muslims have had to deal with textual tensions by differentiating between earlier and later revelations, the Meccan and the Medinan suras.
But aside from very minor heretics, Islam has been clear from very early on that the Quran is not the sole revelation of Islam. There is the example of the sinless and perfect prophet's life and the great mass of his other sayings. His sunna (habitual practice) and the hadith (narration). Which all together give birth to what really shapes Islam, the sacred law code of sharia (pathway).
The famous five daily prayers of Islam? Not in the Quran or even the hadith. Tradition. What the Muslims call ijma, the consensus of the Muslim community. So it seems that even having to hand an apparently self-contained ultra-authoritative book like the Quran does not make for sola scriptura.
Any religious text is interpreted when read. So authoritative interpreters will arise and will teach people how to read the book becoming, despite protestations, a kind of magisterium and Tradition. Certainly true even in Protestantism. Unavoidable everywhere.
Life is messy. So are actual religions.