You could do that by using an animated brush tip (a .gih file) that had the same (or very similar) images for most of the set but had a couple of ‘faded/sparse’ images in the set.
Then use Random selection when Exporting the .gih brushtip file.
However, you would probably need a large set of images to get the effect you’ve shown in the image in your post.
Another way would be to use large Distance variation of Opacity with a few ‘drop downs’ in the curve and use Repeat mode. That would not be random though and the ‘pattern’ might be obvious.
Multiple options come to my mind. Like controlling opacity or flow by “Fuzzy dab” or by “Distance” on repeat. It kinda depends on how much control you want over the gaps.
In some cases, like this one, there are multiple ways to do something with different advantages. Sometimes you have to play around and see what works for you.
Another thing that just came to my mind is adjusting the pressure curve for opacity to fall off pretty steep at some point that even when you lose pressure only slightly the brush barely paints, like when you draw with an old dry ballpoint pen which is about to die.