A single on-camera flash can’t evenly light a large room or outdoor scene at wide angle—this is basically the inverse square law. The foreground will always get much more light than the distant background.

To brighten the whole scene, your best option is to add more light sources. Use multiple flashes placed around the room and trigger them remotely, ideally bounced or aimed to lift the ambient level and keep a more natural look. Outdoors, rely on available light in the environment as well, since one flash won’t light a large open space.

If you want the background to show with available light, use a slower shutter speed—but put the camera on a tripod. That removes camera shake and lets you extend exposure time so the ambient scene records more cleanly, while flash can still light nearby subjects.

So in practice: for short, sharp exposures in big dark spaces, use strategically placed off-camera flashes. For ambient-heavy shots, use slower shutter speeds on a tripod. There isn’t a single-flash solution that will fully light a distant ballroom or outdoor background evenly.