Shouldn't you be asking Acronis?

Yes, we also intuit that the driver was missing at boot, the problem is that DELL does not provide the driver for your hard drive.

As you have mentioned, the operating mode of the controller is set to RAID ON, the other day we chose the AHCI/NvME option and then Acronis did detect the hard drive but the Windows Boot Manager and the Hard Drive with the O.S. disappeared.

You can reconfigure Windows without reinstalling so it will run with AHCI/RAID OFF.

https://superuser.com/questions/1280141/switch-raid-to-ahci-without-reinstalling-windows-10

I haven't used Acronis in years, but it used to be the recovery media ran a version of Linux rather than being a WindowsPE native OS -- if that's still the case, Acronis may have a driver you can use.  

Macrium Reflect is another option -- it builds a WindowsPE OS custom to the system for you (including all the relevant drivers).

Chances are the boot image you're using doesn't have the Intel RST driver needed (if the system is as-shipped from Dell, the drive will be running with Intel RST/RAID ON).

There should be documentation with Acronis on how to include the IRST driver on your boot media (usually made as an ISO file and written to a flash drive).  The default boot media almost certainly will not have the driver you need.

You need the second driver here:

https://www.intel.com/content/www/us/en/download/19512/intel-rapid-storage-technology-driver-installation-software-with-intel-optane-memory-10th-and-11th-gen-platforms.html