Did Og exist or was he a metaphor? I am asking this because we did not find any giant bones in the fossil record as to date. It also doesn’t seem to make sense to me since Judaism is the religion of reason.
R. David Tzvi Hoffman in his commentary to Deuteronomy 3:11 gives a large size for Og based on the bedstead described there. However, he then quotes the opinion of Jean Leclerc (?) that Og deliberately had a bedstead that was larger than necessary, in order for people to think that he was bigger than he really was. R. Hoffman then says that one who finds it hard to accept Og's gigantic size can explain it following this opinion.
תשע אמות וגו' בערך אורך של ארבע מטרים וחצי ורוחב של שני מטרים קליריקוס משער שעוג צוה בכוונה לעשות לו מטה יותר גדולה מן הצורך כדי להיראות לפני בני דורו והדורות הבאים עוד יותר ענקי ומצביע על מקרה דומה של אלכסנדר מוקדון המסופר על ידי דיאוד סיק 95 17 אם כן מי שקשה לו להעלות על דעתו גובה ענקי כזה יוכל לפרש לו את הענין כדעתו של קליריקוס
Thus, if the lack of archaeological evidence convinces you that there was no giant, according to R. Hoffman it would seem that you can just believe that a regular-sized guy named Og existed.
Did Og exist or was he a metaphor?
He most certainly is not a metaphor - note that in Devarim we explicitly reference his bedframe.
Og is but one of the "Refaim", giants mentioned throughout the bible, specifically in Genesis and Joshua. There is no evidence that even humans suffering from gigantism ever grew beyond what we would consider just "tall", and in ancient times this would have not been very tall.
However, the "Refaim" are mentioned in Ugaritic sources, though without any mention of their size. Conrad L'Heureux theorizes in "The Ugaritic and Biblical Rephaim", that the Ugaritic Refaim refer to a class of chariot mounted warriors, that were apparently a rarity at the time. He goes on to hypothesize that the memory of these warriors is reflected in the collective memory as brought down by the biblical authors:
Since these refaim consisted of kings and nobles who fought from horse- drawn chariots, it is only natural that they were remembered as being gigantic in stature — a view which might have been reinforced by speculations on the origins of megalithic structures. The biblical traditions would only have gone off the track when the socio—military category was erroneously thought to represent an ethnic group. Moreover, if we have correctly understood the development, it is altogether possible that the statement that Og, King of Bashan, was among the last of the refaim is historically correct. This item of traditional lore, along with other similar memories which have not been preserved, probably stands at the very beginning of the development which led to the understanding of refaim as an ethnic term.
If that theory is correct, the authors of the books were referring to an old an exaggerated memory of real humans, rather than a metaphor.