Notice that the word for God is capitalized (emphasis mine).
ΚΑΤΑ ΙΩΑΝΝΗΝ 1:1 Greek NT: Nestle 1904
Ἐν ἀρχῇ ἦν ὁ Λόγος, καὶ ὁ Λόγος ἦν πρὸς τὸν Θεόν, καὶ Θεὸς ἦν ὁ Λόγος.
ΚΑΤΑ ΙΩΑΝΝΗΝ 1:1 Greek NT: Westcott and Hort 1881
ΕΝ ΑΡΧΗ ἦν ὁ λόγος, καὶ ὁ λόγος ἦν πρὸς τὸν θεόν, καὶ θεὸς ἦν ὁ λόγος.
ΚΑΤΑ ΙΩΑΝΝΗΝ 1:1 Greek NT: Westcott and Hort / [NA27 and UBS4 variants]
ΕΝ ΑΡΧΗ ἦν ὁ λόγος, καὶ ὁ λόγος ἦν πρὸς τὸν θεόν, καὶ θεὸς ἦν ὁ λόγος.
ΚΑΤΑ ΙΩΑΝΝΗΝ 1:1 Greek NT: RP Byzantine Majority Text 2005
Ἐν ἀρχῇ ἦν ὁ λόγος, καὶ ὁ λόγος ἦν πρὸς τὸν θεόν, καὶ θεὸς ἦν ὁ λόγος.
ΚΑΤΑ ΙΩΑΝΝΗΝ 1:1 Greek NT: Greek Orthodox Church
Ἐν ἀρχῇ ἦν ὁ Λόγος, καὶ ὁ Λόγος ἦν πρὸς τὸν Θεόν, καὶ Θεὸς ἦν ὁ Λόγος.
ΚΑΤΑ ΙΩΑΝΝΗΝ 1:1 Greek NT: Tischendorf 8th Edition
Ἐν ἀρχῇ ἦν ὁ λόγος, καὶ ὁ λόγος ἦν πρὸς τὸν θεόν, καὶ θεὸς ἦν ὁ λόγος.
ΚΑΤΑ ΙΩΑΝΝΗΝ 1:1 Greek NT: Scrivener’s Textus Receptus 1894
Ἐν ἀρχῇ ἦν ὁ λόγος, καὶ ὁ λόγος ἦν πρὸς τὸν Θεόν, καὶ Θεὸς ἦν ὁ λόγος.
ΚΑΤΑ ΙΩΑΝΝΗΝ 1:1 Greek NT: Stephanus Textus Receptus 1550
Ἐν ἀρχῇ ἦν ὁ λόγος καὶ ὁ λόγος ἦν πρὸς τὸν θεόν καὶ θεὸς ἦν ὁ λόγος
John 1:1 Greek Study Bible (Apostolic / Interlinear)
Ἐν ἀρχῇ ἦν ὁ λόγος, καὶ ὁ λόγος ἦν πρὸς τὸν θεόν, καὶ θεὸς ἦν ὁ λόγος.
In John 1:1, suffice it to say that the nominative singular ὁ Θεός can be translated based on context as “the God” or simply “God” (but never “a God/a god”). Thus, “…and the Word was God”, not “a god.” In Greek grammar, if the gender article is left out (making the word non-articular), it does not mean in the least that it will ONLY be translated as “a” god, or “a” fish, or “a” person. This rule applies when the subject or direct object is intended to be non-specific, so context is very, very important. “A man entered the room.” “I saw a man.” Etc. But, “I saw God.” With a linking verb like “to be”, we say “He is God” (Θεός εἶ), not “He is a God.”
Secondly, we need to remember that ancient biblical texts essentially used uppercase scripts. We see this in hand-copied manuscripts and illuminated manuscripts of the Holy Scriptures. There was no such thing as capitalization. Lowercase and capitalization became prominent following the invention of the Gutenberg Press. So, scriptural texts coming out following the 15th century used both lower and uppercase scripts, which became problematic especially with the Lutherans, thus prompting the shift in the German language that we see today, namely, the general capitalization of all nouns, an idiosyncrasy of German.
Therefore, whether a post-15th century reprinted Greek text was capitalized or not is irrelevant. It is simply the preference of the editor or redactor and their arbitrary, “learned” decisions (and clearly not of God!).
The bottom line is that a good command of Ancient and Biblical Greek (especially from a native speaker like myself) indicates that the Johannine prologue is clearly introducing the eternal nature of the Son of God, as Light from Light and God from God, as we profess in the Nicene Creed. Since this Gospel was used as a further catechetical (mystagogical) tool for recently baptized catechumens at Pascha, its intent is not to introduce the absurd teaching that Jesus is yet another albeit powerful eon or spirit (as the Gnostics taught), but the incarnate Second Person of the Trinity (and clearly not a modalistic entity, i.e., appearing as Father in the OT, Jesus in the NT, and the Holy Spirit in the Church.