I am developing Android app on NanoPI M4 using Qt. I need to run app on full screen and I need to get monitor information, physical size and resolution, to draw precise size of lines and shapes and to do correct scaling as requirement.

But app receives completely wrong size and resolution. I asked Qt first this issue and they says that it is because Android OS reports wrong information, I also try to read out the information from DisplayMetrics on Android API, and also it shows wrong values.
I am using Samsung 28 inch UHD 4K Monitor (3840x2160) and Dell 27 inch HD monitor (1920x1080) for my development, and in both case the reported values of physical monitor sizes and resolution are completely wrong (especially for 4K monitor, the values are far small).
I uses the latest android image for NanoPI M4 in FriendlyArms download portal (RK3399-20191228).

Does anyone know why Android reports incorrect values? Is it Android image bug? Or does not support bigger/UHD screen?
Do I need special image? If so does anyone know how to get it? (Or do I need to build android image by myself and how can I do?)