add-custom-product-type.php

<?php
/**
 * Plugin Name: Add custom product type
 * Description: This plugin adds a product type to test PR #33755 (https://github.com/woocommerce/woocommerce/pull/33755).
 * Version: 0.1
 * 
 */
function add_custom_product_type( $array ) {
    if ( is_array( $array ) ) {
        return array_merge( $array, array( 'my-product'   => 'My product' ) );
    }
    return $array;
}

add_filter( 'product_type_selector', 'add_custom_product_type',10, 1 );