How to run virt-manager debian
Write in terminal "sudo apt install virt-manager qemu-system" then press enter. Enter your password
Then press "y". Restart your computer when installation is complete
Run virt-manager
Enter your password
Press "Create a new virtual machine"
Then press "Forward"
Press "Browse..."
And then press "Browse Local" and find OS ISO you want to use
Setup RAM and CPU
Create disk
Select "Customize configuration before install"
Activate virtual network
If you want to change some settings you can do this here
Now you can start standard OS installation