Does the Mac Mini 2018 headphone out also serve as a line-in?

I'm having trouble locating detailed a detailed manual for the Mac mini 2018, only brief information sheets and high-level website pages.

I'm specifically trying to get more details about the "External Microphone" that is shown when I go to System Preferences > Sound > Input. If I do a system report, it says it exists and has one channel.

Does the Mac Mini 2018 headphone out also serve as a line-in?

I'm guessing this is the headphone jack, based on the reply to 3.55 mm Headphone jack 2018 Mac mini. "Also use this port to connect audio equipment to record sound or music, or plug in EarPods to use with audio and video calls."

Take a tour reads "3.5 mm headphone jack: Plug in stereo headphones or speakers to experience high-quality sound while listening to music or watching movies. Or plug in an analog headset with a built-in mono microphone to make audio and video calls." No mention here of line-in vs. mic in.

I thought I read somewhere once that it's line-in, but can't find the reference. And it would be nice if Apple would spell that out in the documentation.

Alas, there is a lack of details as to how to connect to audio equipment to record sound.

Specifically, I want to digitize some old cassettes. They're old cassettes, so I already expect the sound quality won't be great but they have sentimental value and some of the material is not available from streaming services or is personal stuff that I've recorded. That's fine.

I'm getting that, if I'm correct about the input, it will wind up only being mono, but I'm not sure how to accomplish this so I don't lose any content, specifically the left or right channel. (Not an issue for my personal stuff, since I recorded it with a mono mic originally, but an issue for music cassettes.)

Specifically, if my cable has stereo phono at one end (to connect to the line-out on my audio equipment) and a stereo 3.55mm jack at the other end (for plugging into the Mac mini) will the Mac mini automatically do a no-tech mix of the two channels into mono, or do I need to get a mixing cable as well to keep both audio channels?

I realize there may also be phasing issues with one or more recordings when the two channels get mixed to mono, but again I can live with that.

Any clarity on this matter would be appreciated. I'm not expecting magic; I just want to be sure I'm not going to fry either my Mac or my audio exquipment.