Create a new admin user in WordPress via code. Drop this file in the mu-plugins directory and update the variables, then load a page in WordPress to create the user. Remove the file when done.

create-admin-user.php

<?php

add_action( 'init', function () {
  
	$username = 'admin';
	$password = 'password';
	$email_address = '[email protected]';

	if ( ! username_exists( $username ) ) {
		$user_id = wp_create_user( $username, $password, $email_address );
		$user = new WP_User( $user_id );
		$user->set_role( 'administrator' );
	}
	
} );

Would this user still show up in the regular user list for all other admins?

Would this user still show up in the regular user list for all other admins?

Yes, of course.