Hello Roland, thank you for your reply.
We've tried that, but the same result appears. We deleted the RAID 0 volume, changed to AHCI and cleaned up both disk, but "not found any unused disks" error appears again. We tried also change from AHCI to IDE, but same problem appears.
The strage thing about this is when i enter on the shell, with a "lsblk" i can see the disks, and can mount and write on them, but when i return to the installer the problem appears after i press the return key to start the installation.
i've tried all of this also on Qlustar 11 in case of an incompatibility between the RAID controller and Ubuntu 20.04, but same error during install appears.
Also, if this info can help, I found that Intel RSTe RAID Controller is a FakeRaid controller based on software, not a hardware one. On diferent sites I discover that this can be managed by mdadmin, what is installed on the LiveCD. On Qlustar 12 appears the error mentioned in my previous message, but in Qlustar 11 that error doesn't appears.
Regards