I've got YACReader Library running on a home media server PC, which is connected to a 50" 4k HDTV via HDMI. The resolution is 4k x 2k, 3840 x 2160 but it looks like YACReader Library isn't letting Windows scaling manage the app's UI scale at 4k, so all of the text is microsopic on the big screen.
It looks like YACReader Library doesn's support high DPI displays, but is reporting that it does, and so Windows scaling isn't kicking in?
We do support high dpi displays but it is still a work in progress. What's missing in your case is a proper implementation of font size scaling. This bug applies at least to Windows and Linux systems.
My answers are not necessarily official YACReader statements but mostly represent my own opinion in technical matters.
YACReader
