Add custom text to contact form via shortcode WordPress 7

You have a field called "customtext" as the target email address:

[text* customtext]

To get the default value from the shortcode attribute, add the default:shortcode_attr option to the form-tag:

[text* customtext default:shortcode_attr]

Then, add the attribute with the same name as the field ("customtext" in this case) to the contact form's shortcode:

[contact-form-7 id="123" title="Contact Form" customtext="[email protected]"]

You need to register this property beforehand.

Add the following code snippet to your theme's functions.php file:

add_filter( 'shortcode_atts_wpcf7', 'custom_shortcode_atts_wpcf7_filter', 10, 3 );

function custom_shortcode_atts_wpcf7_filter( $out, $pairs, $atts ) {
    $my_attr = 'customtext;

if ( isset( $atts[$my_attr] ) ) {
    $out[$my_attr] = $atts[$my_attr];
}

return $out;
}

Reference link : https://contactform7.com/getting-default-values-from-shortcode-attributes/