(1) No, I did not follow exactly as it said, and l kep the standard setting for State=OFF --> see commented screen shot above. Please confirm.
(2) I learned from your reply, that the interface name retuned by "ifconfig" must be used, instead of the TUNNEL NAME shown in the VPN configuration section. It would be very helpful, to add this hint in the RUTX11-wiki!
Unfortunately, I still was not able to switch OFF OpenVPN!