This looks like JPEG compression artifacts rather than random camera noise. Because your page is mostly dark text on a white background, a noise-reduction filter is usually not the best fix.

In GIMP, try tonal adjustments instead:

• Levels: move the white point inward so the light gray speckles become pure white.
• Curves: lift the highlights and increase contrast to separate the background from the text.
• Contrast: a simple contrast boost may already reduce much of the artifacting.

Why this works: the unwanted artifacts are mid/light gray, while the page background should be white and the text is much darker. By pushing light tones to white, you can remove much of the visible mess without harming the text.

If needed, combine this with a careful threshold-style adjustment, but start with Levels or Curves first—they give more control and are less likely to damage fine detail.

The best long-term solution is to start from a less-compressed source file if possible, since heavy JPEG compression permanently throws away image information.