StVZO bike lights are named as such because they meet the requirements of Straßenverkehrs-Zulassungs-Ordnung, German Road Traffic Registration Regulations. They're specifically designed to shine a focused beam of light that points to the road ahead, rather than emitting a wide beam that spreads outwards and upwards and puts oncoming road users at risk of being blinded.
As with all certifications, just because a light isn’t certified doesn’t mean it’s an issue. StVZO certification is a requirement in Germany. Outside of that market it’s not and as such it doesn’t always mean a non-StVZO light is going to blind everyone else. A good light will use an effective reflector to maximise brightness and battery life. Take care to aim it precisely and it’s unlikely to be an issue. There are also non-StVZO lights that prominently discuss the cutoff characteristics of their lights if you still have a concern.