I have two disks. I install Qubes OS on one disk and decoy OS on the other disk. How to hide Qubes OS disk on decoy OS? On decoy OS, I can see XXXGB encrpted and 1GB of /boot of Qubes OS.
I assume that you have two physical SSDs/HDDs with two different operating systems. In this case, AFAIK the decoy OS will always see all connected hardware, even though it can’t read the encrypted partition. Maybe you could physically disconnect the Qubes disk when booting the decoy system.