I solved this problem, and it goes like this:
At first, I thought this problem was a hardware or serial line problem, but later I tried it with a new line and eliminated these problems. Finally, the reasons for finding this problem are:
The serial ports from the device manager are all above COM 10. If the serial port above COM 10 is changed to 1 or single digits, it must be an idle serial port, so that when the serial port is opened, OK will be displayed instead of ERR.
The specific operation is:
1. Open the device manager, select the port, and right-click "Properties";
2. Open "Port Settings" in the properties and select "Advanced";
3. In "Advanced", there is a "COM port number" item. Select the desired COM port (do not select "In Use"), and then select "Open Serial" in the serial debugging assistant to display "OK".