Hi @LUCA1,
When you were trying to build out the calculated field on the analysis level and were receiving the custom aggregations error, what was the calculated field you were using?
If you have a number of different controls that filter down your visualization, this may be a lot easier to assist further if you can upload a copy of your analysis with anonymized data to Quick Sight Arena; that way we can test out various options to see what may work in this case.