2 Timothy 3:16-17 is the most commonly cited verse that explicitly proves Sola Scriptura. However, being the most commonly cited, it is also the most commonly expected. Opponents usually have a default response locked and loaded, typically "we believe the Bible is inspired too". But I don't think anyone who uses this verse as proof of Sola Scriptura has ever focused on the inspiration. Nor do we necessarily focus on "and is profitable for doctrine, for reproof, for correction, for instruction in righteousness". Rather, what is usually focused on is the bit that is never addressed: the entirety of verse 17!
Anyone can believe that the scriptures are inspired, and are profitable for doctrine, for reproof, for correction, for instruction in righteousness, but those who oppose the doctrine of Sola Scriptura do not believe that it makes the man of God complete or thoroughly equipped for every good work. They usually believe some extra doctrine for which scripture does not equip us.
Catholicism is especially guilty of this. Catholicism has been making stuff up for centuries. None of the uniquely Catholic doctrines can be found in the Bible, including many of what they consider to be "good" works. Veneration of Mary: absent. Obligations: absent. Indulgences: absent. Confession to a priest: absent. The entire Catholic version of the priesthood: absent. The celibacy of the priesthood: literally described as a doctrine of devils (1 Timothy 4:1-3).
With all this in mind, it's simply impossible for a Catholic to read 2 Timothy 3:16-17 and say "I believe this entirely". Rather, they must chop the whole of verse 17 off before such becomes a possibility. By contrast, a Christian who believes Sola Scriptura can look at this verse and say "I believe this entirely". We need not cut anything off, we need not add anything on, we need not change a word. We can practically use this verse to define our position. Therefore, Catholicism is wrong, because its entire structure of authority is in opposition to God.