1. Go to the Detail section in the Lightroom Classic Develop tab
2. Reduce sharpening to just above zero. (If you go all the way to 0, the masking slider is greyed out)
3. Hold down the ALT button while sliding the Masking slider to the right. This will reveal the parts that will be sharpened as white, and the unsharpened parts as black. Adjust this slider so that large sky areas without much detail go black, but the details you want to sharpen stay white.
4. Move the slider to about 60 in the Color section to reduce colour noise (In the video they reduced the radius, too, but I never noticed much effect from that)
4. If the noise still bothers you, move the Luminance slider a tiny bit to the right.
5. Now go back to the Sharpening amount. I usually put it back to the standard “40”, or higher.

The theory of the person in the noise-removal video was to not sharpen the noise in your photo. It is easy to see noise in large dark areas (like night sky), and with the Masking slider, it is easy to remove that.

I have also used the Lightroom Denoise feature, on a 2-second exposure night shot taken at ISO 800,to minimize the movement of a foreground boat in the water, and underexposed 2 stops so as not to blow out the large light source on my main subject. The results of both methods were about the same. On my 7 yr-old laptop, it took about 1/2 hr to use the LR Denoise feature, as apparently it has an inadequate Graphics card for this feature. Also, when using Denoise, I didn’t realize I could adjust the amount of Denoise, so I did 100%.