Greek nouns have Case: Nominative, Genitive, Dative, and Accusative.
The endings change depending on the case. Theon (θεόν) is the accusative case, while Θεός is the nominative case.
The nominative case is the primary case of the subject of a sentence, while the accusative case is the direct object, which tells us something about the subject. The subject is Ho Logos, the Word, so θεόν tells us something about the Word.
So θεόν is not “the ending for the True God” as opposed to Θεός. Your ignorance of the most basic of Koine Greek is astoundingly obvious.
Doug