I’m not sure. I also don’t have anywhere north of 10K objects to test it on.
But in my experience, the reason I’m creating these types of queryString filters is to present some data to a user. The chances that the user actually needs a million objects is very low.
As long as this queryString is the end of the line in any sort of manual pipeline/aggregation, I think you can take advantage of all of the quick Realm functions and then apply it.
Where are you getting the let pathsToFetch: [String] = [...] from? If these are already in Realm like in a List or something, you don’t really need to do this, you can just get the list, but if they are from another source, and you can just send the string, my experience is that the filtering is very quick.