skewed rectangles in Illustrator 29.5, OS 15.4.1, Mac Mini

When using the polygon tool to draw rectangles, Illustrator is giving me slightly unsquare parallelograms. This happens both when specifying the exact size of a rectangle in the popup window or dragging the mouse to create a shape, either within a space defined by guides or not.  Don't know if this coincides with or predates updating Illustrator or OS as both recently occurred. I can't find a setting that controls this. Please help.