Lightroom Noise reduction issue

You can solve it by viewing at 100%, which is the only view that gives you a true impression of the image, because one screen pixel is used to display one image pixel. Any other view will be inaccurate and misleading because the image has been scaled. Always evaluate sharpness and noise at 100%, always apply sharpening and noise reduction at 100%. The same applies to other image detail, like chromatic aberration and moiré.

Library and Develop use different previews, and will not always display identically at magnifications below 100%.

Different applications use different algorithms for sharpening and smoothing when scaling images, and Library and Develop can in this context be considered different applications.

But they should display identically at 100%.