2 Tim 3:15 And that from a babe thou hast known the sacred writings which are able to make thee wise unto salvation through faith which is in Christ Jesus.
2 Tim 3:16 Every scripture inspired of God is also profitable for teaching, for reproof, for correction, for instruction which is in righteousness.
2 Tim 3:17 (HINA) That the man of God may be complete, furnished completely unto every good work.-asv
The appearance of “that” (hina, lit., in order that) at the start of vs 17 identifies what follows as the conclusion to the premise in verse 16.
Reversed it teaches the same thing:
2 Tim 3:17 That the man of God may be complete, furnished completely unto every good work. 16 Every scripture inspired of God is also profitable for teaching, for reproof, for correction, for instruction which is in righteousness.-asv
God revealed to Paul why He wrote Scripture with every verse of it profitable for doctrine, in order that men of God be completely equipped for every good work.
As these Scriptures fully equip men of God for every good work they are able to make Timothy wise unto salvation.
However the OT scriptures can only do this in the context of Christ (The Truth, Jn 14:6), through faith which is in Christ Jesus.
If one accepts the OT testimony Jesus is the Christ (Lk 24:44) and believes in Him as LORD (Rm 10:9) they are made wise unto (eis, into) salvation just as happened to these Bereans:
Acts 17:11 These were more noble than those in Thessalonica, in that they received the word with all readiness of mind, and searched the scriptures daily, whether those things were so. 12 Therefore many of them believed; also of honourable women which were Greeks, and of men, not a few.
Hence the idea Scripture may be “materially sufficient” but not “formally sufficient” is bogus. Scripture is clear enough to be made wise unto salvation.
It may not contain all the info Catholic apologists would like to see, but it certainly does have sufficiently clear material that the man of God be complete, fully equipped for every good work.
God through Paul says so.