Long exposures don’t magically make night look like day; they just collect more light. If the foreground is getting too bright, it usually means there’s more light on it than you want to record—often from moonlight—or the camera meter is trying to render the scene too bright.

A few practical options:

• Use manual exposure and deliberately underexpose the foreground compared with what the meter suggests.
• Shoot when the moon is absent or less influential. Moonlight is reflected sunlight and can make a night scene look surprisingly daylight-like.
• If you truly need a longer shutter speed than the scene allows, a neutral density filter will reduce light at night just as it does in daytime.
• For star trails, stacking multiple shorter exposures is often the better solution. It gives you a long effective exposure, avoids some problems of one very long frame, and is a common technique for trails.

So yes, ND can work, but for star trails especially, planning around moonlight and using stacked exposures is usually the more practical approach.