Support got me the PSD. It doesn't have anything to do with Legacy Compositing (whether I turn off on on in any version).
Basically, the only accurate view of Styles and the image is at 100% view.
I suspect this change was intentional because the behavior you're seeing when scaling the image isn't scaling the pattern accurately in 2020 - whereas 2021 more accurately scales the pattern.
I'll look into it with engineering. For right now, the only way to get the old behavior back is to us
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