How is it +600?


This is normal. The reason the rating changes so dramatically after the game is because you haven't played many games yet and the huge swings is an attempt to figure out your actual rating faster. Imagine if you only gained 8 points per win and you are a Grandmaster opening a new account. You would have to beat a lot of players just to get to your actual rating. By having the rating swing this much, it gets you to an accurate rating faster and it has less people encounter under-rated or over-rated players.
https://support.chess.com/article/210-how-do-ratings-work-on-chess-com

This is normal. The reason the rating changes so dramatically after the game is because you haven't played many games yet and the huge swings is an attempt to figure out your actual rating faster. Imagine if you only gained 8 points per win and you are a Grandmaster opening a new account. You would have to beat a lot of players just to get to your actual rating. By having the rating swing this much, it gets you to an accurate rating faster and it has less people encounter under-rated or over-rated players.
I guess now I know why I'm hardstuck ELO 1500 (On my main and this one)