We noticed the same issue that you had. Our set up is also very similar, except that we use a Sophos Firewall. We have not contacted Sophos support yet in regards to this issue.
However, I'm also thinking that this issue may be related to VLANs. Since I saw something about Windows 11 not supporting Intel Proset for VLANs. I also saw something about 802.1X authentication when I playing around with Windows 11 Ethernet settings. I'm leaning towards VLANs just because if I am at home and use Ethernet with my work computer. There is no issue at all. And I don't have an VLANs set up at home. (Surface Laptop 4 with Surface Dock 1)
It appears that (in limited testing) with a computer off of our domain and that setting turned off, there is no issue with Ethernet connectivity. However, when a computer on the domain is connected to Ethernet, then it starts to have problems. And for some reason the 802.1X authentication button is switched on. (Users are unable to turn this off unless they're an admin. And when you do turn it off, it turns back on within a few minutes). I wondering if it is some GPO setting that is doing this now.