Jpg always has artifacts, it's just a matter of whether they are noticeable and how much we want to consider acceptable. I can see smugding in the panel you showed in a previous comment such as around the GH in slaughter, and on the leftmost character's forehead. I don't consider that problematic though.

The image in the Lemmy post does seem to be jpg, so if you are uploading a png, maybe something is converting it.

Anyway I'm not trying to make your life harder, I appreciate you posting these for us, and can live with imperfection.