Check for update does not work

I've installed 9.0.0.3 and made a manual check for update - but the return is that "I'm using the most recent version" ...

But 9.0.0.4 is there since 25th May ...

Is there no check on low-level changes?

Is there a site where I can see what has changed from 9.0.0.0 until 9.0.0.4 ?

The automatic update check lags behind by a few days on purpose in order to spread out the uptake of updates and to avoid hassling people to update too often, in case two new versions come out in quick succession. (Firefox and other products do the same thing.)

The list of changes can be found in the Release Notes as well as in the Announcements forum.