Is there a way to make the thumbnail look better? I played around with taking out a featured image and adding the thumbnail through layout editor. Doing it this way makes the image quality better. I would have stuck with this but the problem is that the images came out all different sizes. I can add a CSS code to make them the same size but the cropped image isn't centered. So I ended up giving up on that route. The easier way is using a featured image but I was wondering why the quality of the thumbnail gets blurry...
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There is default thumbnail load from media source options, there is an option "Featured image size" please see the screenshot