Dark-frame subtraction works best on RAW data before demosaicing, not on JPEGs or already-converted images. In a JPEG, a hot pixel has usually already been spread into neighboring pixels by demosaicing and processing, so subtracting the dark frame removes the bright center but can leave an obvious black spot.

If you still have the RAW files, use software that applies hot-pixel correction or dark-frame subtraction during RAW processing. That usually gives the cleanest result, and some converters may remove hot pixels automatically.

If you only have processed files, the practical options are:

• use the dark frame as a reference to identify the hot pixels,
• retouch them with a healing brush, clone tool, or content-aware tool,
• or reduce the opacity of the subtraction layer so the black holes become less visible.

For a small number of hot pixels, manual retouching is often the simplest fix. For future night shots, shooting RAW and enabling long-exposure noise reduction in-camera is the most reliable approach.