Add paragraph break after colon in post titles on wordpress single post pages.

gistfile1.txt

/**
 * Add paragraph break after colon in post titles on single post pages.
 *
 * @param string $title The post title.
 * @return string Modified title with paragraph break after colon if applicable.
 */
function modify_post_title_with_colon( $title ) {
	// Only modify title on single post pages.
	if ( is_single() && in_the_loop() && is_main_query() ) {
		// Replace colon with colon + paragraph break.
		return str_replace( ':', ':<br>', $title );
	}
	return $title;
}
add_filter( 'the_title', 'modify_post_title_with_colon' );