Scaling/HiDPI issue for QT5 applications under GNOME

I have a problem with QT applications *(i.e. picard or masterpdfeditor )* under GNOME: their interface looks tiny. Instead, GTK application looks good. I would like a global solution which will work across all applications, not a per-application fix. I don't know exactly where the issue begin (is it a QT5 issue or a GNOME issue?) but I'd like to have a **bigger** interface. ***How can I do it?*** I have already tried with a trick explained here but it works partially: - if I launch the apps directly from the terminal, by appending the right variable e.g. QT_SCALE_FACTOR=1.35 picard, the trick works! - while if I launch them from the menu (gnome-shell), the exported variable is completely ignored . ***Is there a way to fix it?*** I have a laptop connected with an external FullHD 24" monitor. I'm on Arch Linux x86_64 and Gnome 3.28/3.30.