Where do I set the legal notice / Impressum required in my country?

Settings → Author & Publisher → "Legal notice / Impressum". Enter one line per row (name/company, street address, city, contact).

It is printed on the copyright page of every export format: PDF, EPUB, DOCX, Kindle, HTML and Markdown.

Leave it empty to omit it entirely. Some countries (e.g. Germany's Impressumspflicht) legally require this in published books.