libvirt: no connection from host to guest thru nat

[pete-dawgg]

i installed a w11-vm with libvirt and it runs, but there is no connection from the host to the guest thru the virtio-nat interface so rdp cannot connect. The guest can reach (ping) the host's interface thru virbr0, but not vice-versa (which imho is the whole point of nat .) The host can also ping virbr0, but not the guest's ip. Adding a route (to 192.168.122) manually did not help.
The winapps install-script detects the guest's ip correctly, but obviously cannot connect.
What did i miss/get wrong in the networking-config with libvirt?