Low-speed mode is a mandatory built-in function of C2-class drones that caps the drone's ground speed at 3 m/s. It is a technical requirement of the drone class itself — a pilot's promise to "fly slowly" is not a substitute.
Once the pilot has confirmed the mode is active, in the A2 subcategory they may approach uninvolved people to 5 m instead of the normal 30 m. The mode must be switched on before approaching — not mid-approach. It is specifically a C2 feature: on C1 drones no such legal relief exists.