theme-starter-content.php

<?php
/*
Plugin Name: Theme Starter Content
Description: Theme Starter Content Example Plugin
Version: 1.0.0
*/
add_action( 'after_setup_theme', function() {
    add_theme_support( 'starter-content', array(
		'posts'     => array(
			'homepage-section' => array(
				'post_type'    => 'page',
				'post_title'   => _x( 'A homepage section', 'Theme starter content' ),
				'post_content' => sprintf(
					"<!-- wp:paragraph -->\n<p>%s</p>\n<!-- /wp:paragraph -->",
					_x( 'This is an example of a homepage section added by add_theme_support.', 'Theme starter content' )
				),
			),
		),
    ) );
} );