This may be a question for the Viber developers but since Viber for Linux appears to be a Qt5 application I'm asking if someone know how to run Viber for Linux on a HiDPI screen? By default it's tiny and not really usable. All other applications I use seems to work fine with some minor tweaks, but Viber, which I use a lot, is not working right in this regard.
Sorry for "necroposting" but the problem still persists so I'd like to suggest a workaround for everyone still concerned with Viber appearance.
If you need to run Viber (and some other QT apps) on Linux machine with HiDPI screen, try this:
env QT_DEVICE_PIXEL_RATIO=2 /opt/viber/Viber
QT_DEVICE_PIXEL_RATIO environment variable, if set to 2, will make sure the app looks good on a screen with "proper" HiDPI resolution (i.e. screens with "doubled" number of pixels both on x and y axes). Hope it helps.