No — "an" is lowercase in the middle of a title across all major style guides.
"An" follows the same capitalization rule as "a" and "the" in every major style guide. It stays lowercase in the middle of a title and is capitalized only when it is the first or last word.
AP Style, Chicago Style, MLA Style, NYT Style, and AMA Style all specify that articles are lowercase in the middle of a title. "An" is always included in that category, alongside "a" and "the."
The only time "an" is capitalized is when it is the first word of a title, which can happen in genuine titles even if uncommon. The last-word rule would also apply, though "an" rarely ends a title.
Billboard Style capitalizes every word without exception, so "An" would appear in uppercase in entertainment and advertising contexts regardless of its position.
"An" is the form of the indefinite article used before words that begin with a vowel sound. Despite being slightly longer than "a," it is treated identically for capitalization purposes by every style guide.