라이트룸 CC 에서 작업 후 사이즈 축소 방지 방법

From the translation to English:

In Lightroom CC, for example, a file with a size of 25.2 MB is reduced to 10.5 MB size."

I would like to ask you how to make sure that it does not shrink in size.

You don't say what step in Lightroom Classic caused this to happen. If you are exporting a JPG, there is always a change in file size, and that's perfectly okay because JPG is a compression technology. It tries to compress the image in such a way that there is virtually no loss in visual quality. The exported JPG ought to look exactly the same as the original (except for trivial differences).

So there is no problem here, this is what we expect from Exporting to JPG.

Please don't make the mistake that file size is an indicator of image quality. File size does not indicate image quality.