On the hardware requirements it says there the following:
Note: Qubes OS is not meant to be installed inside a virtual machine as a guest hypervisor. In other words, nested virtualization is not supported. In order for a strict compartmentalization to be enforced, Qubes OS needs to be able to manage the hardware directly.
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You may want to try it by installing it on an external disk and that way it won’t interfered with your current windows installation.