Hello [NAME] , the slow write speed is a common issue for the Toshiba XG5 with low capacity.  Dell has a newer firmware for your SSD.  Update yours to see if it can improve the performance.
This KXG50ZNV256G Toshiba NVMe m.2 SSD drive came with the PC, I was trying to use it as a media cache disk and did a benchmark, the write speed is very slow. ( drive specifications is 2,700 MB/s read and 1050 MB/s write, so I am only getting 1/3 of the write speed) I checked in BIOS, it is the AHCI mode for the drive. Internet search led me update the NVMe driver with the OCZ RD400 driver ([URL] but it made no difference. Has anyone seen similar behavior and have a fix? Thanks for reading my post!   .[IMAGE]
XPS 8930, NVMe M.2 SSD very slow write speed