Png does not work with cryptomatte, as it requires a 32bit float precision which PNG can not provide.
You must use EXR in float32bit !
Blender will save out either a OpenEXR or OpenEXR multilayer. If you want all layers in one EXR file per frame, choose the multipayer option.
If you wish to save out multiple EXR per pass (Diffuse, Specular, Crypto ..) you ...
You can try to connect the image (or image sequence) to the denoise node without using the Normal and Albedo sockets but the result won't be as good as it could be.
In general, Intel's OpenImageDenoise is the best option for now, see how to set it up properly: How to properly connect the Denoise node in Compositor?. Alternativly, you can try using other ...
Adaptive Sampling min samples is not the actual amount of samples that cycles is using to render the scene.
From the manual:
The minimum number of samples a pixel receives before adaptive
sampling is applied. When set to 0 (default), it is automatically set
to the square root of the total (max) sample count.
So, what is happening in your case, ...
I will suggest this very easy trick. Remember, this trick will only work for blender 2.81 and above. Go to compositing, and enable nodes. Then, click on add and select search and enter denoising. Then, drag the node to the middle of both present nodes. Something like this:
If you are unable to find denoising normal and denoising albedo, you will find it ...