Just the first steps.

I enabled in engine the incremental backup feature and restarted engine service.

Created a CentOS 8.1 VM to backup, and updated it.

It has one qcow2 disk with flag of incremental backup enabled.

I configured another server to be sort of backup server.

Installed CentOS 8.1 + updates, then

dnf install https://resources.ovirt.org/pub/yum-repo/ovirt-release44.rpm
dnf update
dnf install python3-ovirt-engine-sdk4

dnf install ovirt-imageio-client

Copied backup_vm.py from the examples directory to the /root and tried a full backup

[root@c8-bck-server ~]# ./backup_vm.py full --engine-url https://ovirteng.mydomain --username admin@internal -c ca.pem --backup-dir /backup 80fd995d-63c7-4f2a-a4c2-0ddaf1a8389d
[   0.0 ] Starting full backup for VM 80fd995d-63c7-4f2a-a4c2-0ddaf1a8389d
Password:
Traceback (most recent call last):
  File "./backup_vm.py", line 490, in <module>
    main()
  File "./backup_vm.py", line 181, in main
    args.command(args)
  File "./backup_vm.py", line 195, in cmd_full
    backup = start_backup(connection, args)
  File "./backup_vm.py", line 312, in start_backup
    from_checkpoint_id=args.from_checkpoint_uuid
  File "/usr/lib64/python3.6/site-packages/ovirtsdk4/services.py", line 33584, in add
    return self._internal_add(backup, headers, query, wait)
  File "/usr/lib64/python3.6/site-packages/ovirtsdk4/service.py", line 232, in _internal_add
    return future.wait() if wait else future
  File "/usr/lib64/python3.6/site-packages/ovirtsdk4/service.py", line 55, in wait
    return self._code(response)
  File "/usr/lib64/python3.6/site-packages/ovirtsdk4/service.py", line 229, in callback
    self._check_fault(response)
  File "/usr/lib64/python3.6/site-packages/ovirtsdk4/service.py", line 132, in _check_fault
    self._raise_error(response, body)
  File "/usr/lib64/python3.6/site-packages/ovirtsdk4/service.py", line 118, in _raise_error
    raise error
ovirtsdk4.Error: Fault reason is "Operation Failed". Fault detail is "[Cannot backup VM. Backup is not supported by the host (ovirt01.mydomain).]". HTTP response code is 409.
[root@c8-bck-server ~]#