transfer data from 2014 iMac (thunderbolt 2) to thunderbolt 4 ssd

There is an Apple Thunderbolt 3-to-2 adapter ( Apple – Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter ). It allows you to connect 27" Thunderbolt Displays to modern Macs, and even apparently will allow you to hook up powered Thunderbolt 3 docks to old Macs.

However, there are reasons why it would not work in this case.

• It does not transmit power from one side to another. So even if a portable Thunderbolt 3 SSD did not have a permanently-attached cable, you could not plug it directly into the Thunderbolt 3 side of this adapter. There would need to be an intermediate powered Thunderbolt 3 hub or dock, which would make costs prohibitive.
• A more subtle point has to do with how backwards compatibility works in Thunderbolt. Thunderbolt 4 and 5 accessories are backwards compatible with USB-C (Thunderbolt 3) host ports, but NOT with adapters. Your external SSD is a Thunderbolt 4 SSD and thus NOT backwards-compatible with any Thunderbolt 1 or 2 host, whether you use an adapter or not.

Note that if that portable SSD is a Thunderbolt 4 SSD, it might require Thunderbolt input – in which case you will need to use some other USB drive to copy the data off the old Mac; then move the USB drive to the new Mac, so you can copy the data from the USB drive to the Thunderbolt 4 SSD.

(I've seen SSDs on the OWC site that could fall back from Thunderbolt or USB4 to USB 3.*, as necessary but they appear to be the exception to the rule.)

Using WiFi in not a wise idea. If you want a trouble free migration, PLEASE follow the steps in Setup Assistant and Migration Assistant - Apple Community

Using WiFi for MA is iffy at best. Using your Time Machine or. Bootable Clone backup works EVERY SINGLE Time. If you do not have a Time Machine backup of the old computer, then do that. Operating any computer without backup that is done at least daily is not wise and is a guarantee of losing data.

virtualy wrote:

My wife is campaigning to just give Apple the kids’ inheritance and buy an iMac w a 2TB drive..

Have you thought about getting a modern portable NVMe SSD with a USB-C (USB 3.1 Gen 2) interface? Those are plenty fast enough for many data storage uses, and do not cost a lot more than slower USB 3 / SATA SSDs. Adapter cables that would let you plug a USB-C (USB) device into a USB-A (USB) port – like the USB ports that you have on your 2014 iMac – are not expensive or particularly hard to find.

Some devices that might work here:

• 2 TB Crucial X9 Pro SSD for Mac – $150 at B&H Photo Video
• 2 TB OWC Envoy - $200 at Other World Computing

There's also the 2 TB OWC Envoy Pro FX. This one has an unusual feature. It can work as a Thunderbolt 4 SSD when plugged into a Thunderbolt 4 port, and as a USB SSD (slower speed) when plugged into a USB port. Thus you could also plug it into a USB port on your old iMac (with appropriate adapter cable), and it would run at very high speed on your new Mac.

However, Thunderbolt enclosures do generally add to the cost of an external SSD – and the 2 TB version of this SSD costs $330.

Even if you put a lot of your bulk data onto an external SSD, I would recommend getting at least 512 GB of internal SSD space on the new Mac.

What portable SSD do you have...?

If it support USB-C, then you need a USB-C to USB-A adapter to plug into your old iMac.

Yes, likely will need to use USB.