function savedata() {
	$randomID = uniqid();
	$order_id = rand(1000, 9999);
	global $wpdb;
	$table_name = 'wp_order_quotes_real';
	$countfiles = count($_FILES['file']['name']);
	for ($i = 0; $i < $countfiles; $i++) {
		$filename = $_FILES['file']['name'][$i];
		$upload_dir = wp_upload_dir();
		if (!empty($upload_dir['basedir'])) {
			$user_dirname = $upload_dir['basedir'].
			'/order-quotes/'.$randomID;
			if (!file_exists($user_dirname)) {
				wp_mkdir_p($user_dirname);
			}
		}
		move_uploaded_file($_FILES['file']['tmp_name'][$i], $user_dirname.
			'/'.$filename);
	}
	$dataSubmission = $wpdb - > insert(
		$table_name, array(
			'order_id' => $order_id
			, 'user_id' => $randomID
		)
		, array(
			'%d', '%d
		)
	);
	
	return true;
	exit();
}

add_action('wp_ajax_savedata', 'savedata');
add_action('wp_ajax_nopriv_savedata', 'savedata');

<b>frontend code</b>

$("body").on('click', '#formSubmit', function(e) {
        e.preventDefault();
    	const data = previewAllFields(true);
    	$.ajax({
    		type: "POST",
    		url: ajaxURL,
    		data: {
    			action: "savedata",
    			...data
    		},
    		success: function(data) {
    			alert('Your order has been saved into our database!');
				resetFields();
    		},
    		error: function (error) {
    		    console.log(error, '===error===');
    		}
    	});
    });

Solution - 1

These articles will help you. https://artisansweb.net/ajax-file-upload-in-wordpress/ https://www.phpkida.com/upload-file-using-ajax-in-wordpress/ https://www.ibenic.com/wordpress-file-upload-with-ajax/

Solution - 2

Check if your form have the parameter enctype="multipart/form-data" try to debug your code using print_r($_FILES['file']) and view the structure of the $_FILES array