If you're not seeing the "USB-Serial Controller" entry when trying to use a serial connection on a mac. You probably need the missing driver:
Open the "App Store" and search for "Prolific".
You should find an app called PL2303 Serial.
Click the "install" button.
Click "Open System Settings"
It will tell you installation was "blocked", click "Allow" and confirm with password or fingerprint.
Now try connecting the monitor again, this time you should see it listed: