Another thing to consider is looking at the Dead Sea scrolls you’ll find a bunch of writting like the war scroll that is not in any bible but probably just as important to those people that hid it in the caves as any biblical writting.
Also one clear case of bible tampering is the book of Daniel, the original writtings have another chapter and also the story of Bel and the dragon which is not in the Bible now.
ps. I just remembered another example the 10 commandments. Read what they were before Moses broke them and then read what they are after he gets a new set from god and there is a change or two. Did this really happen in the story or did a scribe make a change or a mistake.