Nikon camera is set to RAW format, and the photos taken are very gray and dark, but the effect of changing to jpeg format is very clear. What's going on here?

Under normal circumstances, what you said will not happen. Automatic default parameters may be used when exporting photos from raw.

Raw is an uncompressed format, which preserves the information of camera photos to the maximum extent. If your ps technology is good, you can reset it in terms of color, contrast, noise control and exposure. The exported photos are better in definition and picture purity than those in jpg format automatically generated by the camera.

My camera has never encountered such a situation. The biggest advantage of raw is that ordinary photos ps will add a lot of noise, but it will not add noise when setting raw. The picture is purer.