Hello! They are synonyms, there isn’t much of a difference, I’d say. Maybe “so forth” is more formal, though. They both mean the same thing - “etc.” Examples: “We will have champagne, cake, balloons and so on.” “For example, the strawberries are red, lemons are yellow, and so on.” => If you wish, check out this link, it may have good and clear examples for better understanding: https://sentence.yourdictionary.com/and-so-forth Have a good day! :)

They are the same thing.

There is no difference. They both have the same meaning: "etc." In fact they are often used combined: "... and so on and so forth."