Perform the "Basic Authentication" request in WordPress with plugin "Application Passwords". Read more at https://maheshwaghmare.com/doc/application-passwords/

basic-auth-request.php

<?php
if( ! function_exists( 'prefix_create_new_post' ) ) :
    /**
     * Create new post with wp_remote_post()
     *
     * @since 1.0.0
     * @return void
     */
    function prefix_create_new_post() {
        $username = 'admin';
        $password = 'mK7M wZmN Fuj5 IKYF XUAv EZ8H';
        $site_url = 'http://localhost/dev.test/';

        $request = wp_remote_post( $site_url . 'wp-json/wp/v2/posts/', array(
            'body' => array(
                'title' => 'Rest API Post 3',
            ),
            'headers' => array(
                'Authorization' => 'Basic ' . base64_encode( $username . ':' . $password ),
            ),
        ) );
    }
    add_action( 'admin_head', 'prefix_create_new_post' );
endif;