I am curious about plural and singular noun usage. Let's assume there were no one who had two computers. (i.e. one computer each.) Which one is more natural: "people have computers," or "people have a computer?"
It depends on the context or the rest of the sentence.
If the sentence is only "People have computers" then that is the most natural way to say it.
If the sentence is "The people have computers" that means the people have many computers. If the sentence is "The people have a computer" that means the people as a group have only one computer for all of them.
If the sentence is something like "Most people have computers" or "Most people will have a computer", then both are equally natural.
Technically, you should strive to make the plural and singular forms of the subject and object match.
Plural: "The people have computers."
Singular: "Everyone has a computer."