VPN RoadWarrior Connection Fritzbox --> IPFIRE --> Ipfire (red) --> Ipfire (blue)

If it is showing as Stopped in the WUI then you can press the button which will be labelled Start OpenVPN Server

This message is because your client has OpenSSL-3.x

You can confirm this on your client by running the command

openssl --version

If it is 3.x and not 1.1.1x then you need to follow the approach in this post/thread
https://community.ipfire.org/t/ovpn-cert-creation-algo/7911/18
of adding into your clients openssl configuration the legacy option.