How to Use Em Dashes (–), En Dashes (–), and Hyphens (-)

> If you want to be official about things, use the en dash to replace a hyphen in compound adjectives when at least one of the elements is a two-word compound.

How is a literal dictionary making fun of people who "wanna be official about things" lol. That's the entire basis for dictionaries themselves

It's Merriam-Webster - they are descriptivist rather than prescriptivist about language. They don't define correct usage per se, but rather document actual usage, though some usage may be given greater weight than others.

In this case, they are calling out the prescriptivist definition but are implying that it may be overkill and offering the more commonly used alternative.