How to connect thunderbolt 2 to thunderbolt 4?

It is by placing the older on in Target Disk Mode. It would also require a rather pricey Thunderbolt 3 (USB-C) to Thunderbolt 2 adapter on top of a pricey Thunderbolt 2 cable.

Transfer files between two Mac computers using target disk mode - Apple Support

Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter - Apple

Apple Thunderbolt Cable (0.5 m) - White - Apple

As a practical matter, I would suggest using an external hard drive. A 1 GB drive should cost less than the adapters/cables you would need for Thunderbolt.

Grant Bennet-Alder wrote:

The most obvious cable for direct computer to computer transfer is the Apple ThunderBolt-3 <-> ThunderBolt-2 cable, US$50 for a one-off transfer.

You may want to look at Target Disk Mode if you pursue that approach:

Transfer files between two Mac computers using target disk mode - Apple Support

That's not complete cable though.

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The Thunderbolt cable is $29 by itself in the US, and the 2 m version is $39.

I guess another possibility is to just put the newer Mac in USB target disk mode and then connect it to the older Mac through a USB-C plug to USB-A plug cable, which I've bought for less than $2 although those typically only operate at USB 2.0 speeds. It might be possible to find a USB 3.0 to USB-C cable though, since some are used for external hard drives. Those cost a bit more, but of course all this stuff is frustrating with USB-C.

The most obvious cable for direct computer to computer transfer is the Apple ThunderBolt-3 <-> ThunderBolt-2 cable, US$50 for a one-off transfer.

You may want to look at Target Disk Mode if you pursue that approach:

Transfer files between two Mac computers using target disk mode - Apple Support

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Do you have a Time machine or other backup drive of the old computer? that would be more straightforward. Or find a drive and make a backup, then move the drive to the other computer.

Migration Assistant can help with that:

Move your content to a new Mac - Apple Support

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Grant Bennet-Alder wrote:

Good point. For this use you would also need that ThunderBolt-2 ThunderBolt-2 cable, that you will likely never use again, at additional expense.

MacBook Pro 2012 and later feature USB-3 speeds on their rectangular USB ports, provided a 9-pin (USB-3) cable is used.

Some people cheap out and buy a mini-DisplayPort cable and it doesn't work for Thunderbolt. Thunderbolt 1/2 reuse the mini-DisplayPort socket/connector, but the cable signaling is supposedly very different.

I tried putting a new Apple Silicon Mac in share mode. Just hold the power button while powering on until options show up. Then go to Disk Utility and then Utilities > Share Disk. Didn't work. It went into the mode. I connected to an older Mac using a USB-C to USB-A cable, and it showed up in System Report as "MacBook Pro" but didn't connect.

But I agree that getting a cable to do this for a one-off proposition may not make as much sense as just finding another way to transfer data, like via Wi-Fi or using a an external drive (including Time Machine).

MID 2012 (non-Retina) has a built-in Ethernet port.

Current MacBook Pro can use an about US$30 Belkin USB-C Ethernet adapter sold on the Apple online store. Cheaper versions (provided they are sold as Mac compatible) can be had for half that price.

The "approved method" for using these is to connect BOTH Macs to your Router with Ethernet cables. Otherwise, the amount of fiddling required to "make it go" is excessive.

Good point. For this use you would also need that ThunderBolt-2 ThunderBolt-2 cable, that you will likely never use again, at additional expense.

MacBook Pro 2012 and later feature USB-3 speeds on their rectangular USB ports, provided a 9-pin (USB-3) cable is used.

One of the best sources for Thunderbolt related gear is OWC https://eshop.macsales.com/

Keep in mind, TB2 is essentially dead and available equipment can be quite pricy.