The sample image below was overly dotted with block spots. How are the spots removed (or at least reduced) using Gimp, please? I have tried the Despeckle filter but it seems to have no effect on the image.
Sorry for working in Krita, but I have a good toolpack installed for it. That toolbox is G'MIC filter collection. It's freeware and it's also available for GIMP (see NOTE1)
I applied G'MIC filter Inpaint:
It despeckles but as a side product here it fills holes. I guess in reality filling holes is the intended main result and the despeckling is a lucky side product because there's not enough black garbage between the letters and lines. That space is seen as white hole which should be filled.
I have not checked what useful basic GIMP with no extras contains for this, but the previous answer by user xenoid hints that some possibilities exist.
Holes in the letters can be restored by inserting the original as the top layer and setting its blending mode = Lighten. The lighter color is shown:
To get perfect letters you need something which recognizes they are letters and replaces them with perfect ones. That's OCR. Nothing ordinary will work because there's so many distorted letters. To be useful the OCR method should be intelligent enough to utilize the context i.e. what word would be the right one. I skip it.
At least one commentator suggests you to erase the garbage manually. He's right. That method doesn't remove any text, but inserting white between the lines makes reading substantially easier.
In a vector graphics program (for ex. Inkscape) you can prepare a set of white rectangles that you duplicate as needed and drag to the right place with no need to mess with layers.
I guess you can easily prepare as groups good white covers for longer chunks than one line. Export the finished page in the wanted format.
If your text has somehow simple and regular line- and paragraph spacing that idea has a possibility to be productive also with bitmap layers in GIMP.
NOTE1: G'MIC is as well available for Paint.NET and Photoshop.