But does port forwarding work for you, can you access your servers from outside your network?
If not, it's probably carrier-grade NAT. There are several ways to fix this:
No, I specifically meant dynamic, because most ISPs only give static IPv4 for business plans, and a dynamic IP is fine if you use a dynamic DNS service (the Fritzbox has one).
Then I don't know, I've set up several Wireguard VPNs on several Fritzboxes and everything works fine.
There is also Carrier Grade NAT, which basically means that you share an IP with other customers, so if you try to access your network from the outside, you will only end up at your ISP's router, where the network is divided up for a group of customers.
There is the Nibelungen saga, a Germanic folk tale. It is too complex to give a short summary. Part of it is the heroic story of Siegfried, the dragon slayer.
It is western and well known in Germany, but judging by the lack of English sources, not very well known elsewhere. For more, I recommend reading the German Wikipedia entry (with translation)