This indeed sounds strange especially since you can download from the Internet faster than you can transfer files between your computers. The speeds should be much greater than that.
From a network perspective, I can't think of any reasons why that would happen, but I did find a
page talking about slow file transfers (between 2 disks or over the network) which affects Windows 10/11. There is a long list of items that can cause that. It may be worth checking out to see if this is a Windows 11 problem caused by one or more issues.