Unregister the post type "Post"

wp-unregister-post-type-post.php

<?php 
/**
 * Unregister the post type "Post" or more
 *
 * @see unregister_post_type()
 *
 * @author Maxime CULEA
 */
add_action( 'init', function () {
	global $wp_post_types;

	$unregister = [
		'post',
	];

	foreach ( $unregister as $post_type ) {
		if ( ! post_type_exists( $post_type ) ) {
			continue;
		}

		$post_type_object = get_post_type_object( $post_type );

		$post_type_object->remove_supports();
		$post_type_object->remove_rewrite_rules();
		$post_type_object->unregister_meta_boxes();
		$post_type_object->remove_hooks();
		$post_type_object->unregister_taxonomies();

		unset( $wp_post_types[ $post_type ] );

		do_action( 'unregistered_post_type', $post_type );

		// Avoid notices
		$wp_post_types[ $post_type ]                     = new stdClass();
		$wp_post_types[ $post_type ]->show_in_menu       = false;
		$wp_post_types[ $post_type ]->publicly_queryable = false;
		$wp_post_types[ $post_type ]->_builtin           = false;
		$wp_post_types[ $post_type ]->name               = false;
		$wp_post_types[ $post_type ]->new_item           = false;
		$wp_post_types[ $post_type ]->cap                = get_post_type_capabilities( (object) array_merge( (array) $post_type_object, [ 'capabilities' => [] ] ) );
		$wp_post_types[ $post_type ]->labels             = (object) WP_Post_Type::get_default_labels();
	}
} );