Hi!
The Windows scaling factor is about upscaling, so if it is enabled essentially every window will appear bigger (but ideally still sharp if DPI-Aware). One cannot have a window that is nonetheless 100% and “HiDPI” at the same time, it goes against the mere notion of HiDPI and the scaling factor.
If you want 100% then turning off HiDPI should be the right solution for you. Usually Windows then round down to the nearest scaling factor, in this case 100% Let me know if this solved your problem! 
Having a local/global custom scaling factor within Cubase has been raised several times on the forum and we will study whether Cubase should with his own scaling factor mechanism.
Cheers