Hello student official answer key by UPSC shall release in the middle of October the dates are not released yet by the authorities.

Some unofficial answer key by various coaching institutes will release soon after the conclusion of NDA examination 2020.

For more details refer to the link mentioned below - https://news.careers360.com/nda-2020-exam-live-updates-know-analysis-answer-key-qualifying-marks-here/amp

Feel free to comment if you've any doubt

Good luck