can only suggest you check in device manager and under the drive's properties>policies that write caching is enabled as if it's off you can encounter degraded drive performance.
I just purchased a 2T Portable Sandisk extreme pro which has a stated transfer speed of 2000MB/s.  Plugging it into my thunderbolt 4 port, I can only obtain max transfer speeds of ~650MB/s write and ~750MB/s read.  The extreme pro isn't thunderbolt but it requires USB 3.2 gen 2x2.  Doesn't thunderbolt 4 support USB 4 which is better that 3.2 gen 2x2.  Why am I not obtaining the stated transfer speed?  NB: I purchased a TB3 cable to be sure it wasn't the cable (got the same transfer speeds).  To test the transfer speed, I'm using a folder that contains 20 files ranging from 1GB to 8GB in size (with 15 of the files being > 5GB each).  Total folder size is 107GB.
Sandisk extreme pro portable hard drive doesn't run at top speed