Yes, my image viewer can set 100% zoom. But my monitor just displays it exactly like if I did open mapy.cz myself on a lowdpi monuitor, and the labels are thus

Yes, my image viewer can set 100% zoom. But my monitor just displays it exactly like if I did open mapy.cz myself on a lowdpi monuitor, and the labels are thus correctly sized and everything just looks very nice, except for a huge canvas with a need for scrolling.