You can create a dimension and use it as a filter. For example
IF((Sales Amount / Budget)>=0.8, 'Meet Target', 'Didn't meet Target')
Then, create an object that would display the stores. You can use Add-ons to show the content of the object when 'Didn't meet Target' is selected.
Extension can also help you to display the Select object as a button instead of filter.
I tried something like that but with a measure:
aggr(if(sum( [Sales Amount])/sum( [Sales Amount Planned])<0.8,1), Shop)
And both that and your suggestion work well (yours better, of course), but I do need some sort of button to make the filter. Why? Because later on I'll need to add other buttons with different special filters that will work on top of every other filter, and the graph/table will change according to each selection. I don't know if that was clear enough, but think of something like this: I'll first use this 80% filter button to show stores who didn't reach the desired threshold, then I'll use another button to show which of those shops sold less, or maybe I now want to show stores that surpassed the 80% threshold, and so on.
That's why I need each of those to be a separate button, and that's why I was wondering if there's an extension to make this easier. Because it seems the default master items won't do.