This is normal Lightroom behavior, not necessarily a misconfiguration. In Develop, Lightroom generally shows noise reduction accurately only at 1:1 (or higher). At smaller zoom levels, the preview may not fully reflect chroma noise reduction and sharpening, so smooth areas like skies can look blotchier than the final output.

That’s why:

• zoomed-out Develop view can show more apparent color noise,
• 1:1 view looks cleaner after noise reduction is applied,
• exported JPEG looks better because the processing is applied to the full image.

Lightroom also relies on generated previews in some views, which can differ from the fully rendered Develop result. If you want to judge noise reduction, do it at 1:1. You can also test by temporarily turning off noise reduction and comparing the 1:1 view to the zoomed-out view.

If you want a closer representation of final output at smaller sizes, checking the image in Library previews or after export can help. But for critical evaluation of noise and sharpening, 1:1 is the correct view.