Romeo's answer covers all the bases, but I thought I'd throw in a practical example, using a DeNoise plugin - this one from OnOne.
Of course you will get better results from a RAW image or indeed just a larger jpg, so this isn't showing it off at its best.
I set this to the minimum necessary to kill the noise, then tried sharpening a little to try grab some detail back. You can immediately see that; yes, it's successfully killed the noise, however it has completely lost any detail from the smoother areas of water near the centre & it's not really doing the sky any favours either.
I wouldn't actually let that put you off trying out the product. It is remarkably good when it's got a bigger/better image to start with.
The only real competition I know of in this area is from Topaz. Both are worth a look at. I tried a Topaz demo a while ago & it was good, but I couldn't justify having both.
There's a comparison guide at Petapixel - ON1 NoNoise AI Versus Topaz DeNoise AI: Noise Reduction Throwdown
No doubt Photoshop will come up level eventually [& perhaps even has already] but my Mac is too old to run the latest AI-enhanced versions, so I cannot test.