Hello dears I have been struggling for a few weeks with this problem since I increased my internet plan from 500 mbps to 800 mbps and when doing a speedtest it gave me between 550 mbps to 650 mbps, sometimes it reaches 700 mbps. I have 2 PCs with Windows 11 pro, both connected by cable and the network cards are gigabit ethernet, when I connect the cable on both PCs the 1000mb link appears, but on both I have the same speed problem, but I have a tp link router deco x20, the router application has an internet speed meter and when I use it it reads up to 815 mbps, so I rule out that the problem is the internet or the router, so on the PCs I did the following:

• Connect the 2 PCs to each other with a direct cable and use the iperf3 application to test the connection between both PCs and it gave me around 600 mbps.
• I did several tests with iperf3 and other equipment and the PCs with Windows 11 did not exceed 700 mbps as a client or server.
• My cables are cat 5 e but made by me, so I bought a cat 6 patch cord and tried connecting a PC directly to the router and the result was the same
• change the network settings and force it to use gigabit and the result was the same
• I updated the drivers of both boards with the latest version and the result was the same
• disable antivirus and firewall
• Disconnect all devices, leaving only the PC that was doing the test.
• check that in the task manager in the performance part that the network was not consuming data in the event that it was downloading an update and there was nothing, it was consuming some kbps
• adjust TCP window handling with the following commands netsh interface tcp show global netsh int tcp set global autotuninglevel=disabled and the result was the same so I put it back to normal
• I did a hard reset of the network using the following commands ipconfig /flushdns nbtstat -R nbtstat -RR netsh int ipv4 reset netsh int ipv6 reset netsh winsock reset and the result was the same
• edit the QoS parameter in gpedit.msc setting the value to 0 to prevent Windows from reserving a percentage of the internet connection and I still have the same problem

I really don't know what else to do and I can't find anything different from what I've already done, and the strange thing is that it happens to me with both Windows 11, I even have a laptop also with Windows 11 home and on this laptop the connection was 150 mbps connected by cable but with the complete restoration of the network, I managed to go up to 300 mbps, even so I am not even halfway there, I don't know if it is some connection control that Windows 11 has but to rule out that it is Windows, I made a pendrive with Ubuntu 20.04 desktop and on one of the PCs I started it in live mode, there I opened Firefox and did the connection test in speedtest and my surprise was that the connection reached 815 mbps, confirming that the culprit was somehow It's Windows 11

Does anyone have any idea what else I could do?