I managed to solve this issue and I hope my solution will help other users.  I had to go to "Device Manager" panel and then manually uninstall the driver of "Thunderbolt controller" under "System Devices". I reboot my pc and from the Dell website I download the updated driver for the Thunderbolt and installed that. Finally the USB-c port started to work again!
Today SupportAssist updated my system and after the reboot my USB Type-C port didn't work anymore. It was connected to an external monitor, but I tried to connect also with a USB memory stick and nothing happens. Instead the normal USB port is still working. These are the updates that have been done: - Dell Inspiron 7391/7591/7791 System BIOS - 1.14.0 - 14,15 MB - Critico - Installato - Intel Management Engine Components Installer - A04 - 318,11 MB - Critico - Installato - Dell SupportAssist OS Recovery Plugin for Dell Update - A00 - 26,24 MB - Consigliato - Installato - Dell Mobile Connect Driver - A00 - 10,59 MB - Consigliato - Installato I suspected the problem was the BIOS so I downgraded to a previous version (1.13.1) but nothing changed.  Do you have any suggestion?
USB type-C port not working