COM4 will be the one - more so because it's using a Prolific chip and only appears when you're plugged in. Is that the port that you checked in device manager as being set at 9600 baud?
Having checked that, it seems like the topic might be a little more involved than it seems to be at face value. Take a read here to see if it helps:
https://stargazerslounge.com/topic/1...200-telescope/
It's been too long for me to remember exactly how I had my LX200 GPS connected to a PC. I had one back when they were new
See if the above link helps. It goes through quite a few steps to try to nail it down.