Adapter usb- c thunderbolt to 2017 Imac thunderbolt 2

Identify the ports on your Mac - Apple Support

"These Mac models have Thunderbolt 3 ports:

...

iMac introduced in 2017 or later"

Is this the drive?

https://www.amazon.com/LaCie-Rugged-Thunderbolt-External-Portable/dp/B0727PN9ZX

https://images-na.ssl-images-amazon.com/images/I/91KqJYztIDL.pdf

"Your LaCie device is shipped with the following cables:

Thunderbolt (integrated on the device): use this cable if your computer has a Thunderbolt or Thunderbolt 2 port.

USB 3.1 Gen 2 (USB-C): use this cable if your computer has a USB-C port.

USB 3.1 Gen 2 (USB-C)–to–USB 3.0/2.0 (Type A): use this cable if your computer does not have a Thunderbolt/Thunderbolt 2 port or a USB-C port."

If the iMac has Thunderbolt 2 The drive's attached cable will plug in. No adapter needed.

If the iMac has Thunderbolt 3, the USB-C to USB-C cable that comes with the drive will plug into the iMac's Thunderbolt 3 port.

Note that this is not a Thunderbolt 3 cable (no Lightning Bolt icon on the plugs).

If the iMac has Thunderbolt 3 and you want to use Thunderbolt instead of USB protocols, you would connect the Apple Thunderbolt 3 to Thunderbolt adapter's Thunderbolt 3 cable into a Thunderbolt 3 port on the iMac and plug the drive's Thunderbolt cable into the adapter. It won't be any faster than the USB-C connectiom:

"While Thunderbolt 2 has the potential to reach transfers rates up to 20Gb/s, the port on LaCie Rugged Thunderbolt USB-C is Thunderbolt, which can reach up to 10Gb/s."

Are you sure you have a 2017 iMac? It has Thunderbolt 3. Maybe you have a 2015 iMac, even if purchased in 2017.

Click the at the top left of the screen and select "About This Mac".

Are you sure the LaCie drive is Thunderbolt 3, not just USB-C? What is the model number of the drive? A non-Thunderbolt USB-C device will not work with the Apple Thunderbolt adapter, even though the plugs will fit.

Yes, it's a Thunderbolt 3 to Thunderbolt 2 adapter. You can find them on Apple's website.