Is this a screenshot from the Preview window or the Contact Sheet? If it is from the Contact Sheet, you'll want to go to the Contact Sheet section of Preferences and enable "Generate high quality thumbnails". If this is from the Preview window, Can you send a screenshot of the full window? When I view a sample image from the Canon R5 in Photo Mechanic, the quality is pretty similar to what it looks like in Bridge. A larger screenshot give us a better look at why you are seeing that quality difference.
