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Qt5 applications can often be run at higher dpi by setting the QT_DEVICE_PIXEL_RATIO environment variable. Note that the variable has to be set to a whole integer, so setting it to 1.5 will not work.
This can for instance be enabled by creating a file
/etc/profile.d/qt-hidpi.sh
export QT_DEVICE_PIXEL_RATIO=2
And set the executable bit on it.