TYPO3 Core

Indexed Search registers the plugin with the 'form' action has not cacheable:

// register extbase plugin
\TYPO3\CMS\Extbase\Utility\ExtensionUtility::configurePlugin('TYPO3.CMS.IndexedSearch', 'Pi2', ['Search' => 'form,search,noTypoScript'], ['Search' => 'form,search']);

If there's not a particular reason, I suggest to remove 'form' action from the not cachable.

Use case: there's a small search form in every page of a website. The searches made with this form are redirected to the search page.
Since the form, even if set as USER, is converted ad USER_INT because 'form' action is not cacheable, extensions like nc_staticfilecache don't cache the pages statically because of the USER_INT.