Not sure if this is specific to macOS, I am seeing weird vertical lines in thumbnail previews of certain Photoshop files. Have not found a specific setting and/or file format (eg color depth, layers/edits, etc) to repro the issue - at this point seems random.
See if doing a "non-destructive change" such as turning a layer off and on will help. It should force the thumbs to redraw on the new system because it is a change you can re-save.
Another thought is to clear the MacOS thumbnail cache using the instructions provided.
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