Need MAC USB Port ID

I’m slowly solving problems one by one! My newer MAC (Big Sur) was unstable with Ground Control.
I’m setting up an older (El Capitan) machine.
It’s asking for my port ID. My new machine auto located it, but this older one doesn’t. any clue how to set Ground Control on older machine?

The easiest way to identify which one is the arduino is to check with it plugged in and then unplug it and check again to see which option disappeared

OK I figured it out. Thank you but it connects then immediately disconnects again and again same as newer machine.

Depending on which usb>serial converter chip your arduino has, you might need this
CH340/CH341 USB to serial port MAC OS driver
or this
PL2303 Mac OS X Driver Download

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