Since events occurring in heaven, and since utterances spoken by God himself, are recorded in the book of Job, it becomes a matter of faith, not historical "proof", that these things actually occurred.
Otherwise, it will be regarded as a "story". This applies to all scripture, not just the book of Job.
There are some other famous (or infamous) books on earth that purport to be 'revelations' to individuals but when I looked into these, as a teenager, I immediately rejected them as they were illogical and were clearly imitations of scripture, not real expressions of the one true God.
But there is not a single verse stated in the entire book of Job that would suggest the narrative is anything other than recorded fact. The assertion that it is a "story" is actually a suggestion that the entire book is a lie. Thus, as I say, it becomes a matter of faith whether one receives that which the book conveys.
Having put almost the entire book into English poetry, accurately in 850 verses, I am familiar with every single verse of it and if there was a hint that it was not stated fact, I think I would be aware of it.
The apostle James makes a statement that I would say is a statement of fact, not of allegorical representation :
Ye have heard of the patience of Job, and have seen the end of the Lord; that the Lord is very pitiful, and of tender mercy. [James 5:11, KJV.]
The end of the Lord would not be 'seen' if the statements were not true facts. The end of the Lord would only be allegorically 'represented', otherwise.