The fully-qualified name for PaginateViewHelper is still TYPO3\CMS\Fluid\ViewHelpers\Widget\PaginateViewHelper, in TYPO3 v9 & v10. But it was faulty replaced in setup.txt by moving to TYPO3Fluid namespace in commit bb0e54e46481680d5e1b47efcbe6736d77b03db0
Please revert
TYPO3Fluid\Fluid\ViewHelpers\Widget\PaginateViewHelper
to
TYPO3\CMS\Fluid\ViewHelpers\Widget\PaginateViewHelper
in
Configuration/TypoScript/setup.txt
The fully-qualified name for PaginateViewHelper is still TYPO3\CMS\Fluid\ViewHelpers\Widget\PaginateViewHelper, in TYPO3 v9 & v10. But it was faulty replaced in setup.txt by moving to TYPO3Fluid namespace in commit bb0e54e46481680d5e1b47efcbe6736d77b03db0
Please revert
TYPO3Fluid\Fluid\ViewHelpers\Widget\PaginateViewHelper
toTYPO3\CMS\Fluid\ViewHelpers\Widget\PaginateViewHelper
inConfiguration/TypoScript/setup.txt