The Relative-Date-Slicer is not able to filter calender weeks due to local week-days.
In my case the week starts on Monday and ends on Sunday.
In my date dimension table in DAX I defined a particular column (WEEKNUM([Date],2)) considering this issue. Then I defined a date column subtracting the latest week number so that I'm be able to set a "Filters on page"-Filter (instate of the Slicer) that filters back in time (in "my" calender-weeksteps).
This work-a-round works in PBI-Desktop but after the report got published to web it indicates errors refering to the column subtracting the week numbers....
Please fix this or develop/deploy some more flexible date-slicer-filter.