Can't get NAT-2 with PS4?

I felt like I tried everything to get NAT-2 with my PS4 because I can't play Borderlands 2 with my friend in Germany.

First I assigned a static IP address to the PS4 and the connection works perfectly.
Most of the tips from the Internet recommend port forwarding to solve the problem. I compared about 10 pages and entered the ports as all pages agreed - without success (yes, router was restarted afterwards).
Next I came across that port forwarding is not necessary if the router supports uPnP. So I deleted the ports and switched on uPnP instead - without success (yes, router was restarted afterwards).
The last tip then said that if a computer was not capable of UPnP, you could use DMZ instead, since this poses negligible risks in the PS4 anyway. So I switched uPnP off again, activated DMZ for the IP of the Playstation - without success (yes, router was restarted afterwards).

None of the measures brought me to NAT-2, now I'm at the end of my Latin. I would be happy if someone else has tips for me to try. The router is a mobile WLAN router Huawei E5573Cs

LTE almost always has carrier grade NAT.

https://de.wikipedia.org/...-grade_NAT

Unfortunately port forwarding is not possible. Unless you use a service like this: http://www.festeip-kit.de/ or: https://www.feste-ip.net/