UPDATE 11/08/2020
Sparky 2020.09 (UEFI mode) rolled forward all the way through up to the time of writing behaves same way on bare metal .
END UPDATE
Due to Libvirt version 6.8.0 there is no more any problems with deployment KVM Guests on EXT4 file system, compare with http://lxer.com/module/newswire/view/290245/index.html
Deploy SparkyLinux 2020.9 ( rolled forward up to 11/08/2020 ) as KVM guest on F33 Server as follows
VM has been deployed in legal BIOS mode on EXT4 filesystems
Issue with Btrfs in Libvirt 6.6.0 has been fixed in Libvirt 6.7.0 release.
Bug fixes : Fix logic in setting COW flag on btrfs
When COW is not explicitly requested to be disabled or enabled, then libvirt should do nothing on non-BTRFS file systems.
See for details http://lxer.com/module/forums/t/36708/
There is no any more any problems with deployment KVM L2 Guests on EXT4 FS
Install KVM
$ sudo apt install qemu-kvm libvirt-daemon bridge-utils \
virtinst libvirt-daemon-system -y
$ sudo apt install libguestfs-tools libosinfo-bin \
qemu-system virt-manager -y
$ sudo modprobe vhost_net
$ lsmod | grep vhost
$ echo vhost_net | sudo tee -a /etc/modules
$ sudo reboot
Install Web Cockpit Console
$ sudo apt install install cockpit cockpit-machines
$ sudo apt install cockpit cockpit-machines
$ sudo systemctl start cockpit.socket
$ sudo systemctl enable cockpit.socket
Tuning firewall
$ sudo apt install firewalld
$ sudo firewall-cmd --add-service=cockpit --permanent
$ sudo firewall-cmd --reload