Is "people" a plural or singular noun? And what other words are similar to this?

Is "people" a plural or singular noun? And what other words are similar to this?

A collective noun that appears in the singular but in the plural
People, police, Castle, etc. are plural in themselves. We can't say a person, a policeman, a head of Castle, the English, the British, the French, the Chinese, the Japanese, the Swiss and other nouns, which are used as plural when referring to the general name of the people, such as the Chinese are industries and branch
Back to the word "people", when it is interpreted as people; people; relatives; families; people or people in a certain place; citizens; civilians, it is a collective noun, which is uncountable, such as
The streets were crowded with people
The men who govern the country are chosen by the people
When people is interpreted as a nation, it is a countable noun
The Chinese people are a brave and hard-working people.
The Chinese nation is a brave and industrious nation
Note: people here means nation and is a countable noun
Chinese people are smart
People here are collective nouns