Answered
100mm in Illustrator 2015 is not 100mm on the monitor?

a rect width is 100mm
but the real with is not 100mm

Illustrator 2022 is right.

a rect width is 100mm
but the real with is not 100mm

Illustrator 2022 is right.
One of the CC versions after 2015 introduced the option 'Display Print Size at 100% Zoom' in Preferences > General. With this enabled, Illustrator will display real-world units at actual size on your monitor. With this option off, Illustrator will display 1 monitor pixel = 1 canvas pixel. Both modes have their uses.
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