Update from 4.0.1 to 4.0.2
From Joomla! Documentation
With 4.0.1 we have introduced an issue into the Joomla Update Component. Please follow this process to update from 4.0.1 to 4.0.2.
You are not affected by the issue when you are updating directly from 3.10.x or 4.0.0 to 4.0.2.
This pertains only to Joomla! version(s): 4.0.1
What is the cause
With the release of 4.0.1 we introduced a issue to the Joomla Update Component that does not allow you to update to 4.0.2 directly. First update a standalone version of the Joomla Update Component and then you are able to update from 4.0.1 to 4.0.2 in the usual way.
How to fix
Then you can go back to Joomla Update and install the full 4.0.2 update.