WPCF7_Shortcode is deprecated since Contact Form 7 version 4.6!

See https://contactform7.com/2016/12/03/contact-form-7-46/

I haven’t used any custom code still it showing this notice.

This answer is confusing to me as well. The post doesn’t explain how to clear the notice. I’m using the shortcode below to display the form on a page. The notice displays in admin and front end. There are no custom functions used anywhere in the theme I developed or in plugins. What needs to be done to clear the notice? Obviously I’ll be disabling debugging but ideally I clear all notices and warnings when updating WP and plugins.

echo do_shortcode('[contact-form-7 id="6"]');

I don’t understand at all

Do you just replace all shortcodes in the site?