Found a way to close it, apparently I am expected to press on the megaphone, the X and the button at the bottom are just cosmetic.
Hello @Turmfalke2, have you seen this issue since initially encountering it?
I haven't seen that window in the last 2 years. Maybe it is displayed only once?
Thanks for the feedback. Closing as outdated.
Nothing extracted yet.
Your system information
25.7.2018
Gentoo
No
Yes
Please describe your issue in as much detail as possible:
There is a fake window that covers a significant part of the screen, pressing x in top right corner does nothing.

Steps for reproducing this issue: