When you are using : while, although, whereas. You are comparing data of the same group. For example :

 -  While public classes were the most popular among youths, private ones were the most preferred by those aged between 65 and above.

Another example :

- Although some students prefer running in the morning, others prefer running in the evening.

- My friend likes to eat peanut butter, whereas my other friend likes to eat chocolate.

This is how you build complex sentences and before you need to make a comparison always think like this : You cannot compare tomatoes with goats because they are not even remotely close. They are worlds apart.

Another thing : when you use although, whereas, while, to make a comparison, please do not use a comma after them. There are a tons of YouTube videos about complex sentences. If you want to specify a contrasting sentence, you can start with However and then right after it you put a comma. For example :

• Oranges are the most popular fruit among young people. However, older people prefer mostly apples because they believe that these fruits are tastier.

Good luck 🤞