Steps to reproduce the issue

Go to Global Config >> Enable Cache
On - Progressive Caching
Cache Handler File

Expected result

Cache should work.

Actual result

Error:

Call stack

Serialization of 'Closure' is not allowed
# | Function | Location
1 | () | JROOT\libraries\src\Document\HtmlDocument.php:474
2 | serialize() | JROOT\libraries\src\Document\HtmlDocument.php:474
3 | Joomla\CMS\Document\HtmlDocument->getBuffer() | JROOT\libraries\src\Document\HtmlDocument.php:804
4 | Joomla\CMS\Document\HtmlDocument->_renderTemplate() | JROOT\libraries\src\Document\HtmlDocument.php:571
5 | Joomla\CMS\Document\HtmlDocument->render() | JROOT\libraries\src\Application\CMSApplication.php:982
6 | Joomla\CMS\Application\CMSApplication->render() | JROOT\libraries\src\Application\SiteApplication.php:754
7 | Joomla\CMS\Application\SiteApplication->render() | JROOT\libraries\src\Application\CMSApplication.php:247
8 | Joomla\CMS\Application\CMSApplication->execute() | JROOT\includes\app.php:63
9 | require_once() | JROOT\index.php:36

System information (as much as possible)

Joomla 4.0.0-alpha12
PHP 7.3.12

Additional comments

Thanks to @cybersalt for reporting this.