length snapping does not get a lot of interest, but i add information on how i solved my problem, in case of somebody might find it useful in the future...
in my case length snapping was not the solution
The cursor movement is not changed; instead, a message is shown based upon the movement of the mouse, so the user can decide when it is time to stop moving the mouse and click the second point
https://vimeo.com/939627532?share=copy
this is low level programming, but it works.