Thanks for the infos. Proxmox is basically debian, I mean, installing KDE or so shouldn't be a problem. Next weekend I'll try at first the proxmox setup, especially interested in performance of the VMs, when using in browser of the same host. And  most probably, it will not be satisfying for a desktop computer setup, so can install qubesos.
Last time I tried QubesOS, several years ago, I was basically using one vm 99% of the time. Do you use the proposed vms? I suppose networking setup doesn't require a rocket science degree...