functions.php

<?php

add_filter( 'option_active_plugins', __NAMESPACE__ . '\disable_acf_on_frontend' );
/**
 * Disable ACF Pro on website frontend.
 *
 * Provides a performance boost if ACF frontend functions aren't being used.
 *
 * @since 1.0.0
 * @link https://www.billerickson.net/code/disable-acf-frontend/
 *
 */
function disable_acf_on_frontend( $plugins ) {
	if ( is_admin() ) {
		return $plugins;
	}
	foreach ( $plugins as $index => $plugin ) {
		if ( 'advanced-custom-fields-pro/acf.php' == $plugin ) {
			unset( $plugins[ $index ] );
		}
	}

	return $plugins;
}