Gentlemen, I would like to thank you for all the help you tried to provide.
Unfortunately nothing could work and some solutions cannot be used because it would be too complex to perform for the owner of that PC.
As a consequence, he is giving up on MSFS and will request a refund tomorrow.
I’m sorry I won’t be able to complete this topic with a nice “Solution” message 
Thanks again to all of you. Your help was really appreciated, no matter the result. 
