The problem ScreenXpert overlaps the main screen when Nvidia MX250 is chosen as main graphics card. The same thing doesn't happen with Interl graphics as primary card.
The solution is to disable the ScreenXpert monitor before the welcome screen loads. In order to do this, open the file
/usr/share/sddm/scripts/Xsetup in an editor and at the end add the following line:
xrandr --output HDMI-1-2 --off