macOS does in fact do this kind of non-integer bitmap scaling. It's got nothing to do with what the GPU is capable of; Apple's UI framework can't do layout or text rendering at anything but "1x", "2x", or "3x" densities.

This is also why the first Catalyst apps looked really blurry and bad on non-Retina displays; Apple applied a non-integer scale to the final rendered frames to work around UIKit not being able to draw the right size widgets.