Starting with the release of Strategy ONE (March 2024), dossiers are also known as dashboards.
STEPS TO REPRODUCE
1. Create a dossier and import external data set from “Clipboard”.

2. Create a grid with an attribute and metrics:

3. Select combo chart visualization.

4. Enable labels for it.

5. Export the Dossier to PDF. After exporting to PDF labels are blurry.

CAUSE
This behavior is expected and it is not a defect.
It happens when there is a black text with white stroke around its border. PDF renders the white stroke with a very bold line, making the text less readable. If the user zooms it in, it will be clear because the white border becomes thinner and thinner.
ACTION
Adjust PDF Viewer options:
Edit -> Preferences -> Page Display -> Enhance thin lines
If Enhance thin lines is enabled, white border of texts will be thicker, so that those texts become less readable, but thin lines will be clearer. In order to make text become readable uncheck Enhance thin lines.
KB441163