Check the Administrator Modules view. Maybe the Cache Cleaner module has been trashed or deleted.
If it is trashed, un-trash it.
If it is not there at all, create a new Administrator Module of type 'Cache Cleaner' and assign it to the 'status' module position.
There are no plans to convert Dummy Content to Joomla 4.
Not enough users and interest in it. And too much work to develop and maintain it to be worth my while.