Report on Tasks by Assigned User across multiple Sheets

Dear all,

I´m familiar with the usage of the 'current user' filter in reports on multiple sheet. This works good as long you want to provide individual lists to the user opening/using a report.

I do look for an option to build a report on tasks categorized by the user assigned. The field 'Assigned To' is not available in the selection for this feature.

Does anybody have an idea?