WordPress Tutorial: In simple steps, going to show you how to remove gutenberg in wordpress 2019 theme. The following codes are tested by using WordPress Child Theme.
Step 1: Open functions.php file (Assuming you are using wordpress child theme)
Step 2: Add this below functions or code
/*==========================================
Disable Gutenberg
===========================================*/
add_filter('use_block_editor_for_post', '__return_false', 10);
Step 3: Save it and you are done