How can I remove noise from a photo?

I think we have to reset this discussion, because we have been talking about the wrong thing all along. What you see here in the screenshots is not noise. Noise looks very different. That’s why Denoise doesn’t work.

Try the following:

1: Turn off denoise, but keep ‘Raw Details’ selected.

2: Set sharpening (same panel, a little bit lower) to zero.

How does the image look now?

I looked at your screenshots and you have set AI Denoise to only 5. It makes sense that you see little or no effect using this extremely low setting. The default is 50. Your screenshot also shows that you sharpen the AI denoised image considerably, using an Amount of 60 and a Radius of 1.2. If you feel the sharpening is too aggressive, then why don’t you use lower values? Finally, your screenshot does not show how much magnification you use, but I get the impression that you have set the view to 200% or even more. At that magnification you will always see a lot of artefacts.

Where is this slider on your Denoise? if you move it to the left, you remove the Denoise action, and if you slide it to the right, you increase the Denoise action. 

What do you mean with the ‘Denoise key’? Denoising in Lightroom Classic is a checkbox in the Detail panel and you can set the amount of denoise with a slider.