A suppressor on a subsonic .22 caliber gun is about as close to movie/video game quiet as you can expect. There is still variation, but subsonic ammo eliminates the "crack" from the sonic boom (comes from the bullet itself), and the suppressor reduces the muzzle noise a lot. In person I've heard one suppressed subsonic .22, and it was about the level of a good clap. 👏

A good answer to your question needs more specifics, but in general, suppressed handguns with home-defense or target ammo are still loud enough to gain attention.

On the other hand, subsonic ammo will be pretty quiet and reduce the noise drastically, but unless you have the semi-auto mechanics tuned properly, the gun won't cycle the next round in very well. I can't speak to the stopping power of subsonic ammo but again, it probably requires specifics to give an accurate answer.