While far from universally accepted, even the most strident critic must admit that the Christian New Testament has a great deal of historical relevance. It is correlated in numerous areas by contemporary first century writings and archeology such that even those who regard it as basically a religious text will still lean on it as a historic reference in some areas.
Not so with the Old Testament. A large portion of the contemporary world - academic and non - considers the Christian Old Testament/Hebrew Tanakh to be purely a work of fiction, borrowing heavily from Egyptian and Babylonian myths.
The earliest existing copies of the documents comprising the Old Testament are hundreds of years removed from the originals, and they refer to events in a time for which very little archaeological evidence has survived. Moreover, there is a scarcity of contemporary literature and writings from surrounding cultures against which these documents can be referenced.
That said, there is far more manuscript evidence surviving for the Old Testament than any other writings of the same time period, and what little archaeological evidence exists from that time period either aligns with Old Testament writings or is subject to interpretation.
Arguing for the accuracy of the Old Testament is a tall task given the overall scarcity of material available for the time it claims to record, however arguing from a lack of evidence amounts to an argument from silence, which is logically unsound. Critics primarily see the Old Testament as mythology because of the numerous miraculous events it records and the ongoing dialogue between God and humans, however there are several reasons why it cannot be categorized as mythology. These are some of those reasons.