H370-HD3 i7-9700 Samsung 970EVO NVMe Boot Problem

[shadowsports]

Good morning,
I have good news, because the problem is solved !!
The cause was, as I suspected  , the SSD disk firmware: corrupt or too old.
I had to work on it a lot, because Samsung Magician didn't detect the SSD disk and that was the only way to update the firmware. The reason for the non-recognition was due to the fact that the SSD was part of a storage pool (probably an automatic setting of O.S. ??).
I deleted the pool with "Storage Spaces" utility and immediately the disc was recognized by Samsung Magician. I updated the firmware to the latest version.
Then I tried to reinstall Windows from scratch.
I loaded the standard BIOS options with CSM disabled, cleaned the disk with diskpartition.
On restarting Windows recognized the SSD disk as a UEFI boot device and the installation finished perfectly.
I thank Shadowsport for the valuable suggestions and patience 
Francesco

Francesco,
Fantastic news!  Now you have a complete understanding of the BIOS features and how they function.  What's left..  you can enable Secure Boot if not already done.  You will then have a fully compliant UEFI GPT formatted boot device. 

Cheers