Well, critical scholars reject that rabbinic tradition about the authorship. The book was written in the much later Persian or Hellenistic period.

To deal with the substance of the book's argument, pious Jews added the epilogue and the tradition that the book was written by Solomon, so that the book can seem to attest only to the futility of godless wisdom.

But the book doesn't reject God. The author isn't an atheist. He observes God's evident absence and the universality of death, which make human life and God absurd.

Do what you can to preserve your illusions, though. Not everyone is fit to accept our existential situation.