redirect_back_to_plugin.php

<?php

add_action( 'wp_after_insert_post', 'redirect_back_to_plugin', 100, 4 );
/**
 * Redirects back to custom plugin page if Post is created with
 * $_GET['go-back-to-plugin'] present.
 *
 * @see https://developer.wordpress.org/reference/hooks/wp_after_insert_post/
 *
 * @param int     $post_id     The post ID.
 * @param WP_Post $post        The WP Post object.
 * @param bool    $update      Whether this is an existing post being updated.
 * @param mixed   $post_before Null for new posts, the WP_Post object prior to the update for updated.
 * @return void
 */
function redirect_back_to_plugin( int $post_id, WP_Post $post, bool $update, $post_before ) : void {
	// This is to bypass the first visit to `wp-admin/post-new.php`.
	if ( is_null( $post_before ) ) {
		return;
	}

	$back_to_plugin = filter_input( INPUT_POST, 'go-back-to-plugin', FILTER_SANITIZE_STRING );
	if ( empty( $back_to_plugin ) || '1' !== $back_to_plugin ) {
		return;
	}

	// Redirect to my custom plugin page with the created `$post_id` in $_GET.
	$redirect_url = add_query_arg(
		[
			'page'    => 'custom-plugin-page',
			'post_id' => $post_id,
		],
		admin_url( '/admin.php' )
	);

	wp_safe_redirect( $redirect_url );
	exit;
}