English is made up of different languages. Folk means the same as people, butit is used differently. In the same way that skin and hide mean the same thing, both words are used. Skin means human skin and hide is the skin of an animal.
The same is true of people/folk. People comes from the French which was spoken by the Norman invaders. Since the invasion French was the only language spoken in court and many aristocrats couldn’t even speak English. Henry V was the first King since the invasion to useEnglish in court. That meant that from 1066- 1386 French was the language of the court and the law.
People is the more formal of the two words. It’s used in legal documents. Folk is more informal, used when one is trying to be more friendly, less formal. That’s why George W Bush was criticised for using the term folk to describe the perpetrators of the 9/11 atrocity.
The short answers folk means the same as people, but is used in a different setting.