NAT behind Mobile Network

Hi,

I have an AVM (Fritz) LTE Router. I am connected to this router via WLAN. My router shows a different IP address as my Browser of my mobile phone. In this case it looks like a NAT connection.

The NextDNS setup pages does me no allow to setup a DynDNS URL which differs from the current connection.

How can I handle this with my AVM LTE  Router?

Thanks Wolle