Yes. In GIMP 2.9, a practical way is to threshold a grayscale copy rather than use Select by Color.

Typical workflow:

1. Duplicate the image, or work from a channel if that better represents the brightness you want.
2. Convert that duplicate to grayscale if needed.
3. Apply a Threshold operation to isolate the brightest pixels/stars above your chosen cutoff.
4. Turn the resulting black-and-white result into a selection or use it as a layer mask.

This works well for astrophotography because you’re selecting by luminance/value instead of by color similarity. If you only need the brightest saturated stars, thresholding a grayscale version is usually the simplest route.