Hello,
I have visited your website and the categories images are displayed in the same quality in which they are uploaded.
Screenshot for Clarification: https://ibb.co/Ksgq96H
Basically the product images and categories images are controlled by WooCommerce and our theme doesn’t influence this.
WooCommerce provides settings for images that you can find under Appearance >> Customize >> WooCommerce >> Product Images.
Screenshot for Clarification: https://ibb.co/kGpzwY8
If you still found that the images are blurry then you can try increasing the image width from the settings.
Best Regards.