Late, but I ponder the same question also when I was implementing App Intent. My conclusion is that the shortcut app somehow knows how to perform the filtering and sorting by itself, hence the list of XXComparator and SortableBy that comes by default and there isn't any sample code that show us how to make custom versions of this.
This behavior is good in such that we get some functionality for free, but it is bad that we can't control the filtering mechanism.
In my app, for the "Find" action, I am able to perform a case insensitive search in my entities(matching) code, but when it appears in the "Filter" action, the search is always case sensitive and there doesn't seems like a way to control it.
What made it frustrating for me also is that, the UI of "Add Filter" in shortcuts app, can't seems to be reproduced by using normal Intent Parameter, and can only be shown as such when we use the EntityPropertyQuery!
Topic:
App & System Services
SubTopic:
Automation & Scripting
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