The notification drawer can only be closed by clicking the bell icon in the masthead a second time (as far as I could discover). I'd expect there to be a close `x` icon in the drawer itself. I was also surprised that clicking outside the drawer didn't close it.
Moving bug to upcoming sprint, will add an issue to patternfly core / react to get an X added to the drawer to close it.
Added issue here: https://github.com/patternfly/patternfly-react/issues/4201
will fix with contribution from upstream when ready moving to upcoming sprint
Update on this, the pf notification drawer has a pr to allow for action when clicking outside the drawer. PR: https://github.com/patternfly/patternfly-react/pull/4587
Created attachment 1712788 [details]
Attached screenshot, this could be verified on 4.6.0-0.nightly-2020-08-27-030439