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.

Then I don't know, I've set up several Wireguard VPNs on several Fritzboxes and everything works fine.

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).

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:

1. Call your ISP and ask them to give you your own dynamic IPv4 address.
2. Use a service like tailscale (also available in Home Assistant)

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)