The design-time preview uses Image rendering.
The preview in the WPF ReportViewer uses XAML rendering, where images will be rendered with standard 96dpi settings. The rest of the content will be displayed via Canvas, TextBlock and etc. XAML elements.
Please check if only images are blurred on zoom, or text (not displayed via image) gets blurred too. Also let us know the machine magnification and resolution settings, and if changing fonts affects the report's preview. Test exporting in PDF to compare the results.
In order to provide you more accurate suggestions, we will need to test the report locally in a similar environment.
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