Your grammar books are quite wrong; the above example is well attested in formal writing as well as informal usage. So is the above as a noun.
No one objects to using prepositional phrases as what used to be called predicate adjectives, and no one objects to a similar use of many bare prepositions:
Sartorius is above all that.
Such behavior is beyond the pale.
I am under the weather today.
The King, my lord, is within, and will be pleased to receive you.
The first officer is below; shall I summon him up?
It would be footling to describe these uses as anything but adjectival.
Old-fashioned writers like me prefer to place such preposition-based modifiers after the noun, which is where normally you place a full prepositional phrase employed adjectivally.
The enemy below
The vista beyond
A car outside
But that is a matter of taste rather than grammar in the strict sense. And there are established idioms in which prepositions are adjectival and do not take the following noun as their objects: through road, inside voice.