You need spice-vdagent

Debian and Kali Linux virtual machines running under KVM/libvirtd lack pre-installed agents like qemu-guest-agent and spice-vdagent, which prevents smooth mouse cursor movement between the guest and host. To resolve this, users must manually install both packages on each guest and reboot the virtual machine.

You need spice-vdagent Debian or Kali Linux installed to as KVM libvirtd guests do not automatically have qemu-guest-agent or spice-vdagent installed. This will prevent seamless movement of the mouse cursor between the guest and host desktop in Virtual Machine Manager requiring the use of a Ctrl-Alt to release the cursor from the guest window . To cure this, install both qemu-guest-agent and spice-vdagent on each guest and reboot the guests . $ sudo apt install qemu-guest-agent $ sudo apt install spice-vdagent