Two different nvidia cards should work, but I don't think it's possible to do it with two cards of the same model.
You can't switch a GPU between host and VM without rebooting, you have to assign one GPU to the VM through kernel boot options, which will hide it from the host.
A lot of people also just use a dedicated (Nvidia/AMD) GPU for the windows VM for gaming and heavy duty things, and only use their onboard Intel GPU for the linux host, which is sufficient for normal usage if you're doing all your gaming through the VM anyway.
I believe it should be possible to use two cards of the same model, using pci-stub instead of blacklisting the driver. I've never gotten it to work, but I also think it should be possible to move a card from the guest back to the host (though that might require some more work on the kernel and/or other components).
This could work with two nvidia based cards ? And when the VM isn't On, the host could use the main GPU ?
Someone share more info about this!