Measurements are not working correctly
If you want to make a new path with 100mm x 100 mm in dimensions and and do that via the transform palette then the path shows an incorrect size (100,013 mm x 100,009 mm) but only if the path has an outline. If there is just a colour filling then the measurement is correct.
That should be corrected quickly.
OS X 10.15.6, Illustrator 24.2.3
1
vote

There's an option 'Used Preview Bounds' for that in Preferences, which toggles the behavior. When it’s on, Illustrator includes stroke weight into dimensions, and does not when it’s off.