¿Cuál es la diferencia entre whereas, meanwhile y on the other hand ?Puedes dar oraciones como ejemplo.

There is some overlap, but generally
Whereas --> It is used to state a contrast in the comparison between 2 scenarios. For example, you can say: John was watching anime, whereas I was working.

Meanwhile --> It is used to show what is happening elsewhere. For example: John was watching anime. Meanwhile, there was an earthquake in Japan.
You can also say: John was watching anime. Meanwhile, I was working.

But you cannot say: John was watching anime, whereas an earthquake happened. (This does not make sense. There is no link). It is like you can compare apples and oranges and state the contrast, but you cannot compare apples to computers. Same thing, you cannot compare what John is doing to an earthquake happening.

On the other hand --> Just use it the same as like その反面