1 Scene > Units > Units Scale $0.001$ , Length > Millimeters
2 Viewport Overlays > Grid Scale $0.001$
3 File > Defaults > Save Startup File
1 Scene > Units > Units Scale 0.001 > Length Millimeters
2 Viewport Overlays > Grid Scale 0.001
3 File > Defaults > Save Startup File
_____ Restart Blender, then
Add > Mesh > Cube Add > Mesh > Cube , Torus, Torus ... open the sidebar to check
ok ^ ^