Slow ethernet speed with Xbox Series X

Hi, i just activated a 1 gbit fiber connection and i wanted to use it with my xbox.

I connected it via cable and the xbox speedtest goes up to only 380mbps.

I tried doing a speedtest on ookla and fast.com on the same xbox via edge and it reaches 700mbps.

I tried resetting and everything, it won't work.

Any help? thanks

:)