I have researched this quite extensively for my wife who insisted we change our air conditioner 3 years ago because it was too noisy. The quietest window-based air conditioner I can find is this one. I live in an apt building, co-op, where split air conditioning is not allowed. I think when I measured it, it was like 47 dB right at the vent at low speed (I just measured it for this post, a unit that is around 3 years old). Moving to the middle of my 350sd ft bedroom, I could barely hear it or notice it was running, it was that quiet. Post-installation, you can add weatherproofing seal around the window, and you may get 1 db less noise.
There are 3 sizes for this AC model.
https://www.amazon.com/dp/B0866Y33PL/ref=twister_B086VZGZDM?_encoding=UTF8&th=1