Is it possible to use a singular verb (makes) when the subject is plural?

Question

Suppose that there is an online app which is interesting because of two main reasons:

1. Its beautiful graphics = X
2. Its pleasant music = Y

Now I want to tell someone that those two reasons make the app interesting. I made a few sentences which sounded wrong to me:

• X and Y are what makes the app interesting
• X and Y are the reason/ reasons the app is interesting
• These features (X and Y) are what made* the app interesting

*Suppose I want to say that in past.

Which one is correct? Can I use any of the above or there is another way to say it, please?

Answer 1

A phrase like "X and Y" can be viewed as two things, or as those two things joined into one. When we think about "X and Y" as being one joined thing then it is possible to say:

Having beautiful graphics and music is what makes the app interesting.

But if we understand them as two different things then we would tend to use the plural agreement

The beautiful graphics and the pleasant music are what make the app interesting.

So if you think that X and Y are two reasons, then use plural agreement. If you think X and Y are one reason, use singular.

(the well-known example is "fish and chips is a popular meal in the UK")