That is the default behavior of Anaplan when you are setting up a Weekly Timescale (4,4,5 ; 4,5,4 ; 5,4,4). You will have to provide the inputs for 53rd week as an when it happens in any Business calendar. As of now there is no way to keep that option Blank or set it as 0, so I don't think there is any way you can ignore 53rd week in Time Settings. The Best you can do is ignore those numbers which fall on 53rd Week or offset those numbers. But if it is about the Week & Year positioning then I doubt it can be done.
I want by Q4 of FY22 to follow 4-5-4 calendar, i,e 26 Aug FY22 to be Month end date and 27 Aug FY22 date onwards should fall under month Sept FY22. I have a line item date format and second line item that derives forecast month from date assigned. So any date till 26 Aug derives a month as Aug 22 which is fine but as FY22 is 53 weeks calendar any date which is 27 AugFY22 through 2 Sept FY22 derives forecast month as Aug 22 which I expect to be Sept 22.