There is a fix for apps that are blurry on the non-primary low-res display. Go to the app properties and on the Compatibility tab click the button 'Change high DPI setting' and check 'Override high DPI scaling behavior' option. Make sure 'Application' is selected in the 'Scaling performed by:' drop-down list.

The blurry apps will render a bit bigger on the non-primary low-res display but everything will be crisp.