Analog casette tape to WAV file via 21.5 inch 2017 iMac
I've tried to copy an analog tape I made many years ago into Audacity on my iMac 2017 21.5 inch desktop computer. The iMac only has one sound port. It says, all I have to do is plug the output from the tape deck into the headphone jack on the iMac and the deck will appear on the list of devices in the system preference, sound window. But it never appears. I play the tape, but the iMac records the sound in the room I'm working in. Is there a third device needed here? Something that would attach between the iMac and the tape deck?
iMac 21.5″, macOS 11.2