So that is not a Thunderbolt 3 device. I see why you think it is a TB3 device:
"LaCie 4TB Rugged Mobile Hard Drive (Thunderbolt & USB 3.1 Gen 1 Type-C)"
However, this is a USB and not a TB3 device, and so the protocol that it supports will be USB and not Thunderbolt. Additionally, as others have noted, it is a Hard Disk Drive, and so its transfer speeds are limited by the hard drive as a hard disk drive cannot come even close to saturating 10 Gbps (your actual speeds are going to be closer to 1.25 Gbps in the best of cases). So it makes no sense for this to use TB3, as this would add a significant amount to the price without any benefit in speed, as again the hard drive means you will get nowhere near speeds to need Thunderbolt 3. (Thunderbolt 3 necessitates additional chip sets, more expensive cables, and an additional certification process.)
Further, even most SSDs on the market are NOT able to effectively use TB3, and you are generally best off with a USB SSD unless you need the absolute extreme edge of speed (which you will pay a steep price for.) Most consumer SSDs use 10 Gbps USB, and most are not able to even come close to using anywhere near the full 10 Gbps.
If you specifically want to use TB3 and want the speeds it enables, you will need a Thunderbolt 3 m.2 NVMe enclosure (which costs between $100-200 without a SSD) and a NVMe SSD to go inside of it. For example:
Fledging Shell Thunder SSD Enclosure (0GB) with Active Cooling - PCIe NVMe Portable External Enclosure m3
www.amazon.com
AND
Learn more about Samsung SSD 970 PRO NVMe® M.2 1TB with the innovative Samsung V-NAND technology and a 5-year limited warranty.
www.samsung.com
That said, there are some downsides to this. You can't easily use this drive on just any other computer, these are larger in size and not as portable, NVMe drives get HOT, and a setup like this costs between 2-2.5 times that of a USB-C 10 Gbps SSD. In sum, unless you are moving massive files nonstop, USB-C SSDs are generally more ideal than TB3.