I've just installed the latest verion of QGIS (3.4.0) on a MacBook Pro 13" (3.3 GHz Core I7) MacOS 10.14. The application seemed to work fine at first. On a certain point I've tried to open a recent project via Project/Open menu and had a system freeze for 12 seconds. During that time the whole system was not at all responsive (just mouse moves did work). None of the other applications worked in any way, I couldn't even move other app's windows, the system monitor didn't show any significant increase of activity and instead of the expected functional filemanager-window a tiny little inactive shadow of the filemanager-window was displayed ... as you might guess in the image below.
I was able to reproduce this behavior for several times - even after restart of QGIS.
The whole thing might be related to QGIS 3.4.0 Madeira: unresponsive but it is on a mac and it doesn't seem to affect the "rest" of QGIS.
... has anybody any idea how to handle that problem ?