Modify CPT URL permastructure

customize-permastruct.php

<?php
/**
 * Plugin Name: My CPT with custom permalink.
 * Description: Change permalink from /cpt/%postname% to /cpt/%post_id%.
 */

add_action( 'init', 'my_cpt_init' );
function my_cpt_init() {
	register_post_type(
		'my-cpt',
		[
			'label'        => 'My CPT',
			'public'       => true,
			'hierarchical' => false,
			'rewrite'      => [
				'slug'    => 'cpt',
				'pages'   => true,
				'feeds'   => false,
				'ep_mask' => EP_NONE,
			],
			'has_archive'  => true,
			'show_in_rest' => true,
		]
	);
}

add_action( 'registered_post_type', 'my_cpt_registered_post_type', 10, 2 );
function my_cpt_registered_post_type( string $post_type, WP_Post_Type $post_type_object ) {
	global $wp_rewrite;

	if ( 'my-cpt' === $post_type ) {
		$wp_rewrite->extra_permastructs[ $post_type ]['struct'] =
			$wp_rewrite->front . $post_type_object->rewrite['slug'] . '/%post_id%';
	}
}

add_filter( 'post_type_link', 'my_cpt_post_type_link', 10, 2 );
function my_cpt_post_type_link( string $post_link, WP_Post $post ): string {
	if ( 'my-cpt' === $post->post_type ) {
		$post_link = str_replace( '%post_id%', $post->ID, $post_link );
	}
	return $post_link;
}

add_filter( 'rewrite_rules_array', 'my_cpt_rewrite_rules_array' );
function my_cpt_rewrite_rules_array( array $rules ): array {
	$obj = get_post_type_object( 'my-cpt' );

	if ( $obj ) {
		$slug = $obj->rewrite['slug'];

		$new_rules = [
			$slug . '/([0-9]+)/page/?([0-9]{1,})/?$' => 'index.php?post_type=my-cpt&p=$matches[1]&paged=$matches[2]',
			$slug . '/([0-9]+)(?:/([0-9]+))?/?$'     => 'index.php?post_type=my-cpt&p=$matches[1]&page=$matches[2]',
		];

		foreach ( $new_rules as $key => $value ) {
			if ( isset( $rules[ $key ] ) ) {
				$rules[ $key ] = $value;
			}
		}
	}

	return $rules;
}