My advice is - have a calendar sheet in your workbook, and use it to calculate any dates matching any criterions you need.

The calendar sheet must have all dates as 1st column, from some start date until some future date (probably about 5 or 10 years in advance). And it may have any number of additional columns, where some characteristics are calculated when the table is created, and then saved as values. Like weekday number, week number (in format yyyyww), month number (in format yyyymm), a column which indicates state holidays (1 for holiday, 0 otherwise), etc.

Now, for your current task, you need to use VLOOKUP() function to calculate a week number from calendar table at date ReferenceDate+n*7 (where n is number of weeks you want to add)

Or, in case you want instead a date of specific weekday returned, you need to use SUMIFS() function to calculate the date in week your referenceStartDate belongs to (with referenceDate and weekday number as conditions), and add n*7 days to result.

And format the column with formula in your table as date.