Yes in Chicago Style and MLA Style — five letters exceeds the lowercase threshold. No in AP Style.
"About" is a five-letter preposition, which puts it above Chicago Style's four-letter lowercase threshold. It is capitalized in Chicago Style, MLA Style, NYT Style, and Billboard Style, but lowercase in AP Style and AMA Style.
AP Style takes the simpler approach of lowercasing all prepositions regardless of length. Under AP Style, "about" is always lowercase whether it appears in a newspaper headline, digital article, or press release.
AMA Style follows AP-style logic and lowercases "about." This means medical publications lowercase it even though book publishers following Chicago Style capitalize it — the same word treated differently by different professional standards.
"About" as the first word of a title is always capitalized in every style guide. It is a common opening word in non-fiction titles and instructional content.
"About" is one of the clearest examples of where Chicago Style and AP Style diverge on prepositions. Chicago Style lowercases prepositions of four letters or fewer but capitalizes longer prepositions. "About" has five letters and is therefore capitalized in Chicago Style.