Thank you for your answer.
Setting up openVPN isn´t that hard - because it has been made easy for users.
It is possible to connect openWRT and the Fritz!Box with VPN - but it has never been made easy.
This guy did it (somehow): VPN Tunnel in Repeater Mode
Here is a “how to” to configure openWRT and the Fritz!Box:
https://www.mundhenk.org/blog/fritzbox-openwrt-vpn
I don´t think it is the right way to import a self configured file into the Fritzbox - to many errors can happen.
It is quite easy to configure a VPN via Andriod/iApple as you can see here:
You only have to add a user to the FritzBox and give him the rights to use VPN.
Fritzbox does not have Travel-Routers - otherwise i would have bought one from them.
There are a lot of Fritzbox users in Austria and Germany who would love to have this feature.
I know many people who have home-automation and want to take a look at it if they are not at home - using the phone is not so comfortable 
I don´t think that many of them know about the possibilities this routers are providing. I found them “accidentally” about a week ago - and it´s a real great gadget!
So please try to impliment this feature to your great “little” routers - It would be great if i could just “switch” vpn on and be connected with my FritzBox.