Sharpening alone usually won’t fix this kind of image. It mainly boosts existing edges, but if the text is low-contrast and softened by JPEG compression, there isn’t much clean edge detail to recover.

A better approach is:

1. Increase contrast first using Brightness/Contrast or a similar tonal adjustment.
2. Then apply sharpening lightly to enhance the letter edges.
3. If available in GIMP, try a wavelet decomposition workflow and boost only the fine-detail layers (small scales) to enhance text edges more selectively.

Why your results got worse: strong sharpening on text often creates halos and makes JPEG artifacts more obvious, so it can reduce readability instead of improving it.

So yes, text images can be sharpened, but they often benefit more from contrast improvement than from aggressive sharpening. If the source image is heavily blurred or compressed, there may be a hard limit to how much detail can be recovered.