Make sure your network card drivers are the proper ones for the hardware and up to date, as well, at both ends. Windows sometimes installs poor drivers, and also recently has a tendency to replace good drivers with poor ones on larger Windows updates.
At least one person got a huge perf uplift from that. The buffer sizes are also worth a try, as per the previous post.
Antivirus and lots of other things outside of Opus also play a part here, so you may need to diagnose the problem 9j your setup to better see where the issue is.
Not necessarily. File Explorer is the one thing everyone tests with, and which is easy to measure speed in, so people tend to notice/complain if something makes Explorer slow. But if something is slow in Opus, it's probably going to be slow in almost everything else as well, e.g. saving documents to the network in Photoshop and so on. (Outside of things which simply call into the same basic file-copy API in the shell which File Explorer uses. You can do that from Opus if you need to, but you lose a lot of functionality.)