It's OK in a formal context, even in writing. But be careful in academic work or other situations where precision is important. In such contexts, I prefer to give specific examples using "such as" rather than leaving the reader to imagine my other examples with "and so on."

Hi Sergio! There is no official rule on whether "and so on" is formal or informal. However, it is not usually used in the formal context because it sounds vague, which can appear to be unprofessional. Still, some people do use it in formal contexts so it depends on who is on the receiving end of your letter/email/message. You may also use "etc." which is commonly used even in formal contexts. However in my opinion, it is as vague as "as so on". An alternative would be to list out a few examples of what you are talking about then add "and many other ____". For example: "At this carnival, there will be stalls selling food, toys, and many other merchandise". You may also say what you are describing in general first then list out a few examples. For example: "This charity event will host a number of talent acts, such as a salsa dance troupe, a guitar ensemble, and a youth choir group." Hope this helps! :)