I have a similar problem to a thread I read that didn't have a resolution that was posted back in Jan 2021. I have 1200gbps service from Comcast and a Orbi Router that my computer is attached to via Cat 6 Cable with no network switches. I just ordered and installed a Realtek 2.5 GBPS network card. I have disabled the onboard Intel Network Card. I have changed my link Speed in network card configurations from auto negotiate to 2,5 Full Duplex and I am still constrained to 1000GBPS. I can go into my router setup and it has a Speed test built in its soft ware and when I run that test it says that the Router is getting 1450 GBPS down and 45 GBPS up, however when I run Speedtest.net on the computer it shows that I can only get 950GBPS. Why is this? I have it ISP an Router is Getting it but computer will not negotiate it and my Link Speed in my properties is stuck on 1000 GBPS. Please help Very confused.