add_term_meta( int $term_id, string $meta_key, mixed $meta_value, bool $unique = false )

function add_term_meta( $term_id, $meta_key, $meta_value, $unique = false ) {
	// Bail if term meta table is not installed.
	if ( get_option( 'db_version' ) < 34370 ) {
		return false;
	}

	if ( wp_term_is_shared( $term_id ) ) {
		return new WP_Error( 'ambiguous_term_id', __( 'Term meta cannot be added to terms that are shared between taxonomies.'), $term_id );
	}

	$added = add_metadata( 'term', $term_id, $meta_key, $meta_value, $unique );

	// Bust term query cache.
	if ( $added ) {
		wp_cache_set( 'last_changed', microtime(), 'terms' );
	}

	return $added;
}