"Απ’ όλα πριν υπήρχε ο Λόγος." is a modern Greek version of the phrase "Εν αρχή ην ο λόγος", which is the beginning of John 1, from the Bible. A much better phrase would be "Aρχικά υπήρχε ο Λόγος".
“πριν” is an adverb of time, not a preposition.
In my opinion, “Λόγος” is wrongly translated into “word” here. The meaning of “Λόγος” was logic/reason. For more information on this you would need to consult a theologist.
Back to your phrase "Απ’ όλα πριν υπήρχε ο Λόγος.", let’s look at the syntax.
“Απ’ όλα πριν” (meaning “before everything”), is a definition of time. “πριν απ’ όλα” is another phrase with exactly the same meaning. Actually the latter phrase is of more typical syntax.
“υπήρχε” (existed) is a verb, past tense of “υπάρχω” (exist).
“ο Λόγος” is the subject, not the object in the phrase.
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Vasiliki Baskou, Instructor/Director, https://learn-greek-online.com.