This is a known issue which according to articles I have read is solved in KB5007262. I am running 22518 and I looked at my update history of Quality updates and I don't see it. I have another post right now where I asked the question, but one of the MVPs suggested that I shouldn't ask it here. Not sure why. I downloaded the KB, but it will not install on 22518. Is that the build you are testing on?
That KB5007262 was for 22000.348 not for development build 22518.
Anyway, there was no fix for this specific problem of write speed degradation on that update.
November 22, 2021—KB5007262 (OS Build 22000.348) Preview (microsoft.com)