page cache

We have an error in the WordPress site showing this "Page cache is not detected and the server response time is slow" Page cache enhances the speed and performance of your site by saving and serving static pages instead of calling for a page every time a user visits. Page cache is detected by...

Since the built-in full page cache in the Magento2 backend is not advised to be used on a production store (only for development purposes), and the other option is Varnish, what are my options to use FPC, for free, on OLS?