Ok, you’ve might have missed what I wrote. Here you find a description how DynDNS can be enabled on a FritzBox:
https://avm.de/service/fritzbox/fritzbox-7590/wissensdatenbank/publication/show/30_Dynamic-DNS-in-FRITZ-Box-einrichten/
Here you find informtion about how to automatically update your DynDNS record on a CloudDNS server. Most likely the https url is right way to go: