Have you checked for new drivers such as for the chipset?  Windows 11 is basically Win 10 right now so not sure why such a situation would develop. There may also be Thunderbolt firmware or drivers involved, has your system had Win 11 added to the drivers versions or any change in this regard.  Other OEMs I have checked have not yet made such a change so the drivers are probably the same. 
I did a clean installation of Windows 11 on my Dell XPS 9370 laptop. It works great when not connected to the docking station. However, when I use the ethernet connected to the TB16, the ethernet drops out every few seconds. I have installed the latest network drivers from the Dell support site for my device, but still have the same problem. In device manager I notice three items have exclamation marks on them, maybe this is part of the issue?
Ethernet unstable with TB16 and Windows 11