Hi @waubau
We appreciate the feedback and would like to highlight that we mean no harm by removing the default Custom Fields metabox. This is not an attempt to “replace” WordPress, it is simply a way to improve load time.
If you’re interested in learning more about the performance benefits, please read this blog post: https://www.advancedcustomfields.com/blog/acf-pro-5-5-13-update/
Enabling the default Custom Fields metabox is easily done with the following PHP code in your functions.php file:
add_filter('acf/settings/remove_wp_meta_box', '__return_true');