Nissan has yet to officially announce the 400Z, let along when its release date will be. But new outlets have been speculating when we can see the new Z car.
Car and Driver
says: "We expect the new Z to debut sometime this year as a 2021 model."
says "No firm date for the 400Z’s unveiling has been given yet. Sources initially suggested a debut this year could be on the cards, but the pandemic could easily cause the launch to be delayed until next year."
Given how hard the Coronavirus has impacted the auto industry my guess is that we won't hear anything about the 400Z until the fall/winter at the earliest.