I'm more familiar with the older Sigs. But, I'm pretty sure the 2022 is a double action/single action pistol that uses a decocker with no additional manual safety. The 250 is a double action only with no manual safety.
The design philosophy is that a long trigger pull that cocks the hammer is enough to prevent accidental discharge, just like a double action revolver, which usually has no safety either.
The decocker is there just to return the hammer to the lowered position and put the pistol back in its double action safe mode.
It's a safe enough system for military and police forces to adopt it where carrying a firearm under stress is common, and negligent discharges are to be avoided.