The system extension is not part of common Composer distributions such as typo3/cms-base-distribution.
Therefore, if you installed TYPO3 following Installing TYPO3, EXT:reports is not automatically installed.
You can install it via:
composer require typo3/cms-reports
For legacy installations that do not use Composer, EXT:reports is already part of the distributed package.
Activate the Reports extension in Admin Tools > Extension Manager.