tsu_newsletter_block/tsu_newsletter_block.php

<?php

// Register Newsletter Custom Post Type
require 'tsu_newsletter_custom_post.php';

// Register Custom Block Category
add_filter( 'block_categories_all',  function($categories) {
    
    // Set Category Slug
    $new_slug = 'tsu-category';
    // Set Category Title
    $new_title = 'To się uda';

    $has_category = false;

    foreach($categories as $category) {
        if($category === [ 'slug' => $new_slug, 'title' => $new_title]) {
            $has_category = true;
        }
    }
    if(!$has_category) {
        $categories[] = array(
            'slug' => $new_slug,
            'title' => $new_title
        );
    };
    
    return $categories;
});

// Register Newsletter Custom Block
add_action( 'init', 'add_newsletter_block' );

function add_newsletter_block() {
    register_block_type( __DIR__ . '/build' );
}