[![enter image description here][1]][1]


[![enter image description here][2]][2]


[![enter image description here][3]][3]


[![enter image description here][4]][4]


[![enter image description here][5]][5]


  [1]: https://i.sstatic.net/UHbfq.jpg
  [2]: https://i.sstatic.net/HCM5P.jpg
  [3]: https://i.sstatic.net/mviCK.jpg
  [4]: https://i.sstatic.net/oJZIT.jpg
  [5]: https://i.sstatic.net/OQnMv.jpg
1 Scene > Units > Units Scale 0.001 > Length Millimeters

2 Viewport Overlays > Grid Scale 0.001

3 File > Defaults > Save Startup File

_____ Restart Blender 

Add > Mesh > Cube , Torus ... open sidebar to check

ok ^ ^