Sub sonic ammo is quieter but in a semi-auto, there may be a chance of jamming as there isn’t enough oomph to eject the shell.
Yes. When I was a teen I would shoot shorts in a .22 semi-auto for late season squirrel hunting. It was as quite as a pellet gun and no “krack”. I could often get 2 or 3 shots before the squirrel caught on. I had to load them 1 at a time and manually eject the casing.
That is why I only shoot subsonic from a bolt action. It's frustrating when the semi-auto fails to cycle. My wife has a Ruger Deerfield 44mag rifle. She purchased some "Cowboy Action Shooting" 44mag ammo. It didn't produce enough gas to cycle the action. She fired it. No brass. Cycled the bolt. Out popped the expended brass. It turns out the rifle needs a real 44mag round in the weight range of 200 gr to 240 gr to properly cycle.