Wordpress - When importing - failed to import: Invalid post type feedback

The issue is you're trying to import posts with a post type of feedback, but there is no such post type registered on your install of WordPress.

Quick-and-easy fix is to register one:

add_action( 'init', function () {
    register_post_type( 'feedback', [
        'public' => true,
        'labels' => [
            'singular_name' => 'Feedback',
            'name'          => 'Feedback',

Place it in your theme's functions.php, or in a MU plugin (eg. wp-content/mu-plugins/feedback.php).

The Jetpack plugin creates a custom post type of feedback when active. You may need to just install that plugin first (as I did). Cheers!