I would like to update you: the technical service has resolved the problem.
With this command line given by the command prompt, the program quickly opened:
cd "C:\Program Files\Simplify3D-4.1.2"
then I had to set "compatibility mode" in Tool>Options>Visualisation tab... as you had initially suggested. I restarted the software and now it works.
But I didn't have to change the register that way.
Thank you all, but I thank the technical service that solved me. I leave this track for those who encounter the same problem because in this way for me it was decisive and very simple to realize.