@zekkendo ty for the tip. Turns out my data-saver setting wasn't working, so I had to reset cookies to get it to work and to actually disable properly.
Another way to do this is to look at the image source. For example:
https://mangadex.org/data-saver/31b3480946f9db785aac4fe27cbb0c6e/6-2d91fdca34d276dfdf8a1a5aae8017c320001f3f62905b20a3bea0e70daaecf3.jpg
vs
https://mangadex.org/data/31b3480946f9db785aac4fe27cbb0c6e/6-2d91fdca34d276dfdf8a1a5aae8017c320001f3f62905b20a3bea0e70daaecf3.jpg