On MacOS the Lightroom Classic Rendering Area appears to show a non Retina rendering on a Retina screen.

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No, that option is set to off. LrC should use the original file.

Agreed.

To narrow down where the problem might be, if you delete the smart previews for a couple of those photos (Library > Previews > Discard Previews) and restart LR, does the problem go away?

nice

Unfortunately, I’m not seeing those symptoms with your sample photos on my Macbook Pro (2023, 16” retina, Mac OS 26.4.1). I’ve tried importing several times and restarting LR. If Adobe can’t reproduce the behavior, they’re not likely to pay attention.

You could try doing Preferences > Performance > Camera Raw Cache Settings > Purge Cache, on the theory that the cache is misbehaving. That sounds like a stretch, but it’s trivial to try.

The screenshots indicate that the image is a combination of Original  + Smart Preview. Make sure that LrC has access to the Original otherwise you’ll get the sawtooth effect when zoomed in.

​@johnrellis Here is another example. This time with a file from the X100VI. Screenshot and linked original below:

https://we.tl/t-gqi2wow6b2a0gvua

I don’t see these symptoms on my Macbook Pro (2023, 16” Retina) or the external 4K display. Without a sample photo allowing Adobe to reproduce the problem, they’re very unlikely to pay attention.

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If you share the original image (not a screenshot or export), we can see if the issue is specific to your computer or occurs on other installations.  If the forum won't let you attach the file here, upload it to Wetransfer, Dropbox, Google Drive or similar free service and post the sharing link here.