Being restricted to just using username () in measures (or AllowedRowsExpression) means that you cannot use the context of the current user in slicers or page level or report level filters. Just ...
I found a way to implement this using a Bridge table. Here is the article on how to do it. https://medium.com/@barrasa8/dynamic-data-masking-in-powerbi-based-on-rls-927eb6a34e5d
