PHP: WordPress: How to add a classic block as a default.

wps_enable_gutenberg_classic_block_for_all_post_types.php

<?php


add_filter( 'allowed_block_types', 'wps_enable_gutenberg_classic_block_for_all_post_types', 10, 2 );
/**
 * Adds a default Classic block if no default content exists for all post types.
 *
 * @param bool|array $allowed_block_types Array of block type slugs, or
 *                                        boolean to enable/disable all.
 * @param \WP_Post $post The post resource data.
 *
 * @return bool|array
 */
function wps_enable_gutenberg_classic_block_for_all_post_types( $allowed_block_types, $post ) {
	// Add a classic block.
	global $initial_edits;
	$initial_edits = array(
		'title'   => $post->post_title,
		'content' => $post->post_content ? $post->post_content : '<p>Add content here</p>',
		'excerpt' => $post->post_excerpt,
	);
	
	// Return whatever allowed blocks was.
	return $allowed_block_types;
}

wps_enable_gutenberg_classic_block_for_one_post_type.php

<?php

add_filter( 'allowed_block_types', 'wps_enable_gutenberg_classic_block_for_one_post_type', 10, 2 );
/**
 * Adds a default Classic block if no default content exists for one post type.
 *
 * @param bool|array $allowed_block_types Array of block type slugs, or
 *                                        boolean to enable/disable all.
 * @param \WP_Post $post The post resource data.
 *
 * @return bool|array
 */
function wps_enable_gutenberg_classic_block_for_one_post_type( $allowed_block_types, $post ) {
	// If not our post type, bail.
	// Change my_post_type to post to enable only for posts.
	if ( 'my_post_type' !== $post->post_type ) {
		return $allowed_block_types;
	}
	
	// Add a classic block.
	global $initial_edits;
	$initial_edits = array(
		'title'   => $post->post_title,
		'content' => $post->post_content ? $post->post_content : '<p>Add content here</p>',
		'excerpt' => $post->post_excerpt,
	);
	
	// Return whatever allowed blocks was.
	return $allowed_block_types;
}

wps_enable_gutenberg_classic_block_for_some_post_types.php

<?php

add_filter( 'allowed_block_types', 'wps_enable_gutenberg_classic_block_for_some_post_types', 10, 2 );
/**
 * Adds a default Classic block if no default content exists for a specific set of post types.
 *
 * @param bool|array $allowed_block_types Array of block type slugs, or
 *                                        boolean to enable/disable all.
 * @param \WP_Post $post The post resource data.
 *
 * @return bool|array
 */
function wps_enable_gutenberg_classic_block_for_some_post_types( $allowed_block_types, $post ) {
	// If not our post type, bail.
	// Change [ 'post', 'page', ] to be whatever post types you want.
	if ( ! in_array( $post->post_type, [ 'post', 'page', ], true ) ) {
		return $allowed_block_types;
	}
	
	// Add a classic block.
	global $initial_edits;
	$initial_edits = array(
		'title'   => $post->post_title,
		'content' => $post->post_content ? $post->post_content : '<p>Add content here</p>',
		'excerpt' => $post->post_excerpt,
	);
	
	// Return whatever allowed blocks was.
	return $allowed_block_types;
}