I don't use USB on the router, but I have a NAS which was also slow. It turned out it was because Windows 11 24H2 ENFORCED smb signing. That works fine when connecting to a real PC with a modern processor, but NASes and routers have very small CPUs and they can't handle the extra work. Turning off smb signing in Windows helped a lot.
You can try the same, if it doesn't work just reenable it again.
Here's a link describing it: Disable smb singing in Windows 11
You can try the same, if it doesn't work just reenable it again.
Here's a link describing it: Disable smb singing in Windows 11