I think the problem was with a windows update.  I upgraded my Windows 11 and boom, 3300MB/s read 1600Mb/s write. Thanks everyone for your suggestion.
I just bought a new Inspiron 3891. It has a sk hynix bc711(oem only). It is a NVMe, and I benchmarked it using CrystalDiskMark. The results were very slow. 899Mb/s write, 700Mb/s read. It is a 256Gb ssd. This should not happen. From my knowledge, a NVMe should have atleast 2000Mb/s read and write. Why is this happening? Latest drivers, bios. Please give me a solution. I have searched the whole internet  
oem NVMe slow speeds