Qubes OS is a security-focused operating system, the core idea behind how Qubes provides security is an approach called security by compartmentalization.
This approach focuses on limiting the damage an attacker can do by separating your activities and their related files into securely isolated compartments called qubes you can think of them as virtual machines (VMs).
Qubes uses a “Type 1” or “bare metal” hypervisor called Xen. Instead of running inside an OS, Type 1 hypervisors run directly on the “bare metal” of the hardware. This means that an attacker must be capable of subverting the hypervisor itself in order to compromise the entire system, which is vastly more difficult.
Although you certainly could use any of the virtual machine technologies out there to set up multiple VMs on your regular desktop, that kind of arrangement can end up being pretty clunky and less secure.
There also are all kinds of mistakes you could make with that kind of set up that would eliminate any security benefits you might get in long run instead give Qubes OS a try.