if someone play two games at the same times, can i report that player?

Technically, if one game is white against stockfish/strong bot/strong oppponent and the other is black against an opponent, and you are playing the same moves in the game against the strong opponent as your opponent is playing in the other game, and vice versa, you could probably be considered cheating.

Yes. It's not for nothing that lichess forbid you from creating a new game while you're playing another one.

The only way to create a second game is when you are playing black and your opponent has not yet made the first move. But it doesn't look like a feature, rather a bug, vulnerability, flaw.