I am working on a 4K laptop that is regularly connected to a full HD screen (with the internal screen disabled when an external screen is connected(. Every time I (dis)connect the screen, the DPI scaling changes between 100% and 200%. Gtk3 applications adapt to this just fine, but applications written in Qt do not – they keep using the scaling factor they were started with. That is, if I start a Qt application in high DPI mode, it looks way too big when switching to low DPI, and when I start the application in low DPI mode, it looks way too small in high DPI.