I've seen a lot of these advice float around and these are not international laws. Even in a neighbour country like Canada, these don't apply completely. There is no law in all provinces where employers can't add a clause to block employees from talking about salary. Likewise, in Canada, it's common law that you give “reasonable notice”, which is based on your position, how long you've been there etc. The tit for tat is that the employer will give severance based on your position, how long you've been there etc.
TLDR: Legal advice in this subreddit is almost always America focused. Please check your local laws. People who give advice should mention what country's law they are talking about.