Why does my Chess.com minus 500 points from my blitz rating after one game that I lost?
The site uses the Glicko rating system that includes a measure of rating uncertainty called the rating deviation (RD) value. Players with few games in a pool will have a high RD value and see larger rating changes after games. As more games are played that value decreases as does the magnitude of rating changes.
https://support.chess.com/en/articles/8566476-how-do-ratings-work-on-chess-com