My desktop PC is quiet in idle and even while gaming (absolutely most of the time, depending on how many things are going on): The AMD X3D CPU is all cores undervolted using BIOS's PBO feature + a Macho CPU cooler, and a dedicated GPU is at -45-50% power, all in an open case. Only if the CPU utilizes like more than 4 threads, do I hear the fan.
If you need a room with 0 guaranteed noise, where also the water cooling fans would have to be outside, then this makes sense.