Sandisk Extreme pro SSD external hard drive but only can get 1000 MBps

"There has been quite a few reports of slower USB-C native external drive performance, but much better Thunderbolt3 performance!

There is a sizable I/O difference between the two USB-C connections! A Thunderbolt3 cable is capable of transferring up to 40 gigabytes of data per second, which is twice the maximum data transfer speed of USB-C. However, in order to hit these data transfer speeds, you must use a Thunderbolt cable with a Thunderbolt port, and not a USB-C port, and lastly the device must be a Thunderbolt drive.

USB C vs Thunderbolt 3 Explained"