The fact that Jesus was in the beginning is in the OT. There is a verse in one of the books to the effect that Jesus played amongst God’s creation. However, it is not expressly manifest; more so, it is implied.
In English the expression “through someone” means that without the action of that person the end effect could not have been achieved.
Therefore Through Jesus everything can be accomplished, without HIM we could achieve nothing.
Another possible understanding is that Jesus Christ is the bridge between God and his creation. The Father is in heaven, infinitely far away, but Jesus, as the Word which was made flesh (John 1:14), is in creation as he is in the Father, (John 14:20) and is therefore the perfect mediator. Therefore, “All things came to be through him” (John 1:3).
Edited to add: Similarly, our prayers are heard and answered “through Christ our Lord.”
Yes, I get all that, but I’m thinking that since the Resurrection, Christ is eternally God and man, transcending time and therefore “retroactively” present as Word made flesh before creation. It’s a bit like a time-travel paradox.