Creation and modification dates are by default only related to actual files.
If you want that applied to tasks as well, then you need to add dates to the actual tasks, and reference those dates in your queries. I don’t think that’s a viable way, unless you are auto-creating tasks, or something like that.
So the query you’ve written does return any tasks from files that has been modified the last 2 days. The error in that query is incomplete. Try with either !completed or status = " ". You’re not guaranteed that it’s the tasks which have changed, it could very well be that some other text that has changed. But if a task has changed, that query would pick up that as well as other changes.