Rules for writers, Tenth edition - Diana Hacker, Nancy Sommers 2021

Capitalize titles according to convention
Capitalization
Mechanics

In both titles and subtitles of works mentioned in the text of a paper, major words such as nouns, pronouns, verbs, adjectives, and adverbs should be capitalized. Minor words such as articles, prepositions, and coordinating conjunctions are not capitalized unless they are the first or last word of a title or subtitle. (In APA style, capitalize all words of four or more letters. See 63a.)

Capitalize the second part of a hyphenated term in a title if it is a major word but not if it is a minor word. Capitalize chapter titles and the titles of other major divisions of a work.

Seizing the Enigma: The Race to Break the German U-Boat Codes

A River Runs through It

Titles of works are handled differently in the APA reference list. See “Preparing the list of references” in 63a.