An issue with Windows 11 is slowing down certain NVMe SSDs and it has been first spotted months ago when the system was still in beta stage. The problem hasn't been fixed since then and was recently brought to light once again by a number of Reddit users. As a result, Microsoft has finally acknowledged the issue and is already working on a fix.
In fact, the company is actually pretty close to releasing a patch. In a support document, Microsoft outlines the reason behind the slow-downs and it says it's related to the NTFS USN journal and the triggering of unnecessary actions each time a write operation occurs. Interestingly enough, the USN journal is always active on the C: drive.
The Optional Update KB5007262A is supposed to fix this and should be available pretty soon and given how widespread the problem is, it's highly recommended that you install the update, especially if you are running the OS from a speedy NVMe SSD.