The game studio claims the game is ready and has all content in it, but they're still working on raising the quality bar. CD Projekt Red explains they undercalculated the time they needed for the improvements that will be delivered via a Day 0 patch. Furthermore, the company's statement says the biggest challenge right now is that they're shipping the game on 9 platforms simultaneously, which results in a lot of preparation and testing work.
As such, another 21-day delay to December 10th is necessary.
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— Cyberpunk 2077 (@CyberpunkGame) October 27, 2020