Enable accessibility mode in widget as default

All enabling Accessibility Mode does is add a class to the admin body. The styles and script behaviour change based on that class. So if you want to make accessibility mode the default, you can add that same class if the user hasn’t set accessibility mode on or off:

add_filter( 
    'admin_body_class', 
    function( $classes ) {
        $widgets_access = get_user_setting( 'widgets_access' );

        if ( empty( $widgets_access ) ) {
            $classes = $classes . ' widgets_access';
        }

        return $classes;
    }
);