Collect the default WordPress user fields for the Bioraphicall info (discription) and Website URL (user_url).

default-wordpress-website-and-biographical-fields.php

<?php
/**
 * Add Website and Biographical Info to Membership Checkout
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */

function my_pmprorh_default_wp_user_checkout_fields() {
	if ( class_exists( 'PMProRH_Field' ) ) {

		// Create custom checkout box area.
		pmprorh_add_checkout_box( 'additional', 'Additional Information' );

		// Start fields
		$fields = array();

		// Conditional to show only on frontend. Useful for WP default fields already on user edit profile page.
		$your_profile = is_admin() ? false : true;

		// user_url field
		$fields[] = new PMProRH_Field(
			'user_url',
			'text',
			array(
				'label'    => 'Website',
				'size'     => 40,
				'profile'  => $your_profile,
				'required' => false,
			)
		);

		// description field
		$fields[] = new PMProRH_Field(
			'description',
			'textarea',
			array(
				'label'    => 'Biographical Info',
				'size'     => 40,
				'profile'  => $your_profile,
				'required' => false,
			)
		);

		foreach ( $fields as $field ) {
			pmprorh_add_registration_field( 'additional', $field );
		}
	}
}
add_action( 'init', 'my_pmprorh_default_wp_user_checkout_fields' );