Truncating Headlines by words count in Schema Plugin https://schema.press/docs/truncating-headlines/

schema-truncating-headlines.php

<?php //* do not include php tag

add_filter('schema_wp_filter_headline', 'truncating_headlines_words_567545256');
/**
 * Schema Plugin: Truncating Headlines by words count
 *
 * @since 1.0
 */
function truncating_headlines_words_567545256( $headline ) {
	
	$word_count = 6; // number of words

	$short_headline = wp_trim_words( $headline, $word_count, '' );
		 
	return $short_headline;
}