You can find the secret achievements online. I will tell you some of them: Defeat an opponent in 10 moves or less , win with less than a second remaining , checkmate by castling , win without loosing any pawn , play 20 daily games at the same time etc. I hope I helped.
secret awards

thx but i wanted to say how to play 20 games at once i can only do 6
It's apparently Daily games, not Live. I stopped playing Daily by the time the achievements were released, so I've never seen it.

There's also the Killer King achievement: Checkmate the opponent with a king move (castling works too)

You can if you move the king out of a piece's way and create a discovered mate on the enemy king. Very rare opportunity to come across though.

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🏆Complete Guide to Achievements : Regular Edition🏆
what are all the secret awards?