In the "Filters" tab I am only able to filter by:
Tasks with no due date
And what about "Priority 4"?
Priority 4 is the default priority every task has if you don't set a priority to it. We've added these 3 by default as they represent the custom priority level and any often searched for, but you can of course add the "Priority 4" filter there.
To do so, simply tap on "Manage filters" then "Add filter" and set a query for "priority 4" (or just "p4") and you can save it and use it anytime.
OK, that's fine. Thanks for your quick answer.