Hi Sonia, I’m a bit confused about this, maybe because I’m not a Windows user, but why would you want PsychoPy to use anything other than the native resolution of the display? You can get stimuli to appear at a given size in cm as long as the appropriate information for the display (physical size, pixel dimensions, and distance) are entered in the Monitor Centre.
Perhaps you could give us a specific example of what is going wrong for us to help with? This scaling sounds like just an OS setting for presenting interface elements at consistent sizes across different displays and is likely not really relevant at all to PsychoPy.