GL-X3000 - Cellular connection issue

[SpitzAX3000]

Here it is

GL-X3000 Telekom Germany

I have problems to get 5G connection with the GL-X3000 Spitz. LTE works, but this is very slow. I’m using German Telekom sim. I tried it in a IPhone and it’s working and very fast (around 300Mbit) but in Spitz it’s 50-70 max. As APN i tried the standard internet.v6.telekom. This not working at all with Spitz. internet.telekom works, but slow. How should I configure to have the 5G connection with highest speed? Thx for helping