Thanks for all your help and endless patience (Except for the last comment). Eventually I found the ports menu to learn that I have a Silicon Labs CP210x to UART bridge (Com 11), which I already knew from the fact that I am running an ESP8266. How this helps me retrieve the Com port 10 that I am missing, and why my sketch used to run on port 10 and now won't access the serial monitor on Com 11, I will probably never know.
I'm truly grateful for your effort, which is more than anyone else did, but I'm going to pass on the stamp collecting or fishing. This group is called, "Newbie Corner" for a reason. You are clearly a well qualified computer person. You might consider spending your time scanning the other topics, which would be more in keeping with your talents.