This article is about books. Book royalties are generally considered self-employment income, not passive income, under the tax code.

> However, if you hold an operating oil, gas, or mineral interest or are in business as a self-employed writer, inventor, artist, etc., report your income and expenses on Schedule C (Form 1040).

https://irs.gov/publications/p525#en_US_2021_publink10002292...