For the moment, ports above COM10 are not named COM10. They are named \\.\COM10 and so on. Except that some drivers use names like USB port 1 for all ports. Don't forget to double \ chars when inside quotes. E.g. "\\\\.\\COM10"
Manually edit the virtual machine's configuration file (.vmx on Windows hosts, .cfg on Linux hosts). Change the following line from:
serial0.fileName = "COM10"
serial0.fileName = "\\.\COM10"
Power on the virtual machine to verify the COM10 serial port is operational.