If you want to use as little plugins as possible to prevent possible hacks/etc, you can disable 2 plugins by using the following codes. Add them into your Functions.php file of your wordpress theme and enjoy.
PHP in Widgets
add_filter('widget_text','php_in_widgets',100); function php_in_widgets($html){ if(strpos($html,"<"."?php")!==false){ ob_start(); eval("?".">".$html); $html=ob_get_contents(); ob_end_clean(); } return $html; } add_filter( 'widget_text', 'do_shortcode' );
Classic WP Editor
add_filter("use_block_editor_for_post_type", "disable_gutenberg_editor"); function disable_gutenberg_editor() { return false; }