If you run qemu from CLI you get a window which grabs keyboard and mouse automatically. Ctrl+Alt+G (from the top of my head) releases the input devices so you can again navigate the host. The window is otherwise a default window for you display server.

I find qemu from CLI way more transparent then these GUI-Applications since each vm is a readable, single script. So I recommend this.

Regarding installation on iMac bare metal: If the kernel supporta virtualization you can expect to work flawlessly. If you have a dedicated graphics card you can only pass this (as well as dedicated devices like hdd's) if you main board supports IOMMU.

If it does all you need is the qemu man page to setup your vm.

Why I prefer a qemu script to any GUI alternative:

The entire script for passing RAM, GPU and a HDD is about 10 lines max. A default vm with tcg-emulation e.g. via libvirt etc. can pass 50 lines of xml easily.

I recommend giving it a try. My workflow is: Place the install script in some directory. The default run script is placed in my ~/.bin/ You can combine these scripts but I find it way simpler to separate them (you would need more elaborate options mounting devices).