Whenever there's a major new operating system update, some issues are bound to pop up. So far, the Windows 11 release has been relatively smooth, but a problem has popped up that could cause issues for Windows 11 and Intel's Killer networking software.
Microsoft is aware of the issue and is actively working on a fix. In the meantime, if you upgrade to Windows 11 and are using Intel's Killer networking, you might see some slowdown thanks to User Datagram Protocol (UDP) packets dropping in certain situations.
Here's what Microsoft had to say about the problem on its known issues page:
Compatibility issues have been found between some Intel Killer networking software and Windows 11. Devices with the affected software might drop User Datagram Protocol (UDP) packets under certain conditions. This creates performance and other problems for protocols based on UDP. For example, some websites might load slower than others in affected devices, with videos streaming slower in certain resolutions. VPN solutions based on UDP might also be slower.
Fortunately, you won't have to wait too long for the fix, as Microsoft says it hopes to have one ready in time for the October security update, which is set to drop on October 12, 2021. So as long as you can hold off on updating to Windows 11 until then, you shouldn't have any problems.
If you're not sure whether your system has an Intel Killer NIC, you can check the Device Manager under Network Devices. Under there, you'll see any Killer devices listed, which will let you know if you should wait for the patch before getting Windows 11 up and running.