Hi there.
I don't think this is in relation to issue #9090.
That one had to do with the internal mechanisms of doing blocking IO with timeout.  this is done internally by using non-blocking sockets and select(), and the backport dealt with some edge cases on windows where select() could falsely indicate that data were ready.

From what I can see in this error description, we are dealing with real non-blocking IO, i.e. an application is using select and non-blocking sockets.

It is possible that this windows edge case is now being elevated into the application code and whatever select() logic being used in rpc.py needs to be aware of it, or that for some reason this socket is supposed to be blocking, but isn't.

I'll have a quick look at idlelib and see if I can see anything.