With the update to WP 5.8 and WC 5.6 the "woocommerce_product_categories_widget_args" filter no longer works, which hook should I use to be able to customize the new product categories block widget?
The solution mentioned in this post Hide subcategories from woocommerce category widget it worked before upgrading to WP 5.8, and it still works if I install the Classic Widget plugin, but I want to use the new block widgets available from WP 5.8 version without using Classic Widget plugin:
how should i do?
You have to use the Classic Widget plugin, or you need to write your own code. The current widget block, that displays the categories, does not have any filter hook points included, that allow you to modify it.
Your last resort option may be to extend the class ProductCategories in the Blocks src folder, which is now responsible for rendering the list.