Xbox series X is Not working well with new Router

Hi there, i tried alot at this Point and i cant find a solution myself.

The Problem:

Before i got the Vodafone Standart Router (black) Connected via LAN and everything was fine. Not great tho but i guess that was a Xbox Download Server Problem.

Now i "Upgraded" to the ultrahub 7 also Connected via LAN. When i start a Download or Go to the Xbox Store or want to start a Game i get very often a non loading response or i Case of starting a Game a Time Out because it took to Long. In the mean time if i Go to the Network settings at the Same time where the Problem ist, i get good results in Case of DLSpeed latency Open Port and so on. But it wont start the Download even taking Up to 3min after i click Download before it Shows in the Queue.

What i tried:

First was reboot / hard reset everything

I tried via WLAN

I tried every Option inside the Router from what i know, Like upnp and other stuff.

I tried the cloudflare and Google DNS

But nothing works

If someone has a clue what IT could be. Pls let me know i can share Pics If needed.

Thx