This involves some principles of the disruption and recovery of the third-order Rubik's cube. For example, if you flip a Rubik's cube in situ, you must flip another Rubik's cube (or three or five Rubik's cubes ...), so that the state of the Rubik's cube will be correct.

Therefore, after the first two layers are restored, the top cross block must be even (including zero), not odd.