i don’t think the system is really designed to allow you to find all observations, excluding the ones annotated dead – at least not in one step. finding these would require at least 2 queries – one to find all observations with out an alive/dead annotation, and a separate query to find observations with an alive/dead annotation not including dead.
it’s not super intuitive (and some people think of this as a bug), but you you can see the discussion here for more details: https://forum.inaturalist.org/t/identify-filter-without-annotation-not-working-properly/30148.