Installer window is too small (or test is too big) when using scale 200%, please have a look to screenshots.
I reproduced this issue on a clean Ubuntu 19.04 and 19.10 in a virtual machine (VirtualBox) and on a hardware.
Tested on the Change Installer UI Example.
Perhaps it is already fixed in Qt 5.14 (
Update: I reproduced the issue with Qt IFW 3.2.2 built by Qt 5.14.2.