Great! I think the issue is that you are effectively doing a search based on yes/no, and that search needed to either be in the search panel, or via a filter search, rather than just sitting within an expression.
Separately, when looking at your data structure (having a list of notifications within the user field), this discussion came to mind: Alternative approach to the Bubble’s recent tutorials for list of things You may have already seen it, but it gets into pros/cons of having longer lists within a datatype.