You can add non-cacheable block only to custom pages. In other case, magento Page Cache will not work for these pages OR update information in block via ajax (magento section requests).

Some things described here [https://mirasvit.com/blog/magento-2-page-cache-coverage-rate.html][1]


  [1]: https://mirasvit.com/blog/magento-2-page-cache-coverage-rate.html