Hi @giovannialbe ,
>>>> I can't find the midpoint command
There is no such command in AutoCAD.
Do you mean one of the Object Snap modes?
If yes, then you can specify Midpoint object snap at a prompt for a point, you can do one of the following:
- Press Shift and right-click to display the Object Snap shortcut menu

- Right-click and choose an object snap from the Snap Overrides submenu

- Click an object snap button on the Object Snap toolbar

- Enter MID at the command prompt
If you mean midpoint between two points (MTP) command modifier, you can find it in the Object Snap shortcut menu or in the Snap Overrides submenu or enter MTP at the command prompt when AutoCAD asks for point input.