Thanks for the indication, I found, looking around, the command to unlock all compatible Mac versions, but I hadn't used it.
I managed to re-enable the sidecar function but only when I connect it via usb, but it doesn't work. It connects, enables, showing the lateral service icons on the iPad, but the central screen remains black and after a few seconds it writes an error message on the iPad window and on the Mac.
I tried to insert the commands in the terminal, but no effect has changed, neither on the enabling via Wi-Fi, nor on the functioning.
But am I the only one to have these problems or nobody is trying to use Sidecar with any version of Catalina? It would be comforting for me to know that there are common problems and that therefore we have to wait for new Beta or that someone will discover some cause and solution.
Thanks and greetings to all.