Had the exact problem. Took me a few to realize that caching was turned off on some of my external drives. Pop into Disk Managment and see if that’s the problem. If that looks good, then make sure the ports are what they need to be (3.x). If that’s all good, then go into safe mode and see what happens.
If all else fails, ask Copilot. ;)
Good luck!
Other suggestions: https://thegeekpage.com/fix-slow-file-copy-speed-in-windows-10/