how to postpone certain holidays that fall on weekend

I live in a country, where by law, certain holidays are not allowed to fall on a weekend. If they do, they need to be delayed to fall on the first available working day.

For example, the holiday of Saint-X always falls on the 19th day of April. If that day is a Saturday or Sunday, this holiday needs to be celebrated on the first free working day (not necessarily Monday - especially when Monday already hosts a different holiday). There were cases in the past when such a weekend-ish holiday needed to be postponed by 6 or even 9 days.

I'm having a hard time coming up with a formula to implement this simple rule. In my spreadsheet, I have a column A with regular holidays and column B with holidays that are required to be postponed.

Column C contains dates of days, and column D (expected output) should fix column C's special holidays.

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spreadsheet

EDIT:

So far I got this far, but it is a nasty draggable formula with INDIRECTing that is not so ideal:

=IF(COUNTIF($B$3:$B$100, C3)=0, C3,
  WORKDAY.INTL(C3-1, 1, "0000011",
  FILTER({$A$3:$A$100; $B$3:$B$100; INDIRECT("D$3:D"&ROW()-1)},
        ({$A$3:$A$100; $B$3:$B$100; INDIRECT("D$3:D"&ROW()-1)} <> C3 )
    *LEN({$A$3:$A$100; $B$3:$B$100; INDIRECT("D$3:D"&ROW()-1)}))))

Converting it to LAMBDA:

=BYROW(C3:C30, LAMBDA(x, LET(a, A3:A30, b, B3:B30,
 d, INDIRECT(ADDRESS(3, COLUMN())&":"&ADDRESS(ROW(x)-1, COLUMN())), 
 IF(COUNTIF(b, x)=0, x, WORKDAY.INTL(x-1, 1, "0000011",
 FILTER({a; b; d}, ({a; b; d}<>x)*LEN({a; b; d})))))))

With this I'm still failing to implement circular_reference-free recursion via LAMBDA. Hope someone can help.

You may try:

=LET(a, TOCOL(A2:A, 1),
     b, TOCOL(B2:B, 1),
     c, TOCOL(C2:C, 1),
     d, FILTER(c, MATCH(c, a, 0)),
     e, BYROW(b, LAMBDA(x, IF(WEEKDAY(x, 2) > 5, WORKDAY(x, 1, c), x))),
     f, VSTACK(d, e),
     SORT(SCAN("", f, LAMBDA(x, y, IF(COUNTIF(f, y) > 1, IF(x = y, WORKDAY(y, 1, c), y), y)))))

This outputs a sorted version of your expected results and works with Iterative calculation turned off.

OUTPUT

UPDATE

If the mapping of dates is important for future use, you may also try:

=LET(a, TOCOL(A2:A, 1),
     b, TOCOL(B2:B, 1),
     c, TOCOL(C2:C, 1),
     d, MAP(c, LAMBDA(x, IFNA(XLOOKUP(x, a, a), IF(WEEKDAY(XLOOKUP(x, b, b), 2) > 5, WORKDAY(XLOOKUP(x, b, b), 1, c), XLOOKUP(x, b, b))))),
     SCAN("", d, LAMBDA(x, y, IF(COUNTIF(d, y) > 1, IF(x = y, WORKDAY(y, 1, c), y), y))))

• This outputs your expected results now and works with Iterative calculation turned off.
• It leverages using the XLOOKUP function to return matching dates of Column A if Column C's dates are found in Column A.
• Afterwards, it checks if the dates of Column B are weekends with WEEKDAY, and if they are, finds the next working day with WORKDAY.
• The SCAN function is then used with COUNTIF to identify duplicate dates and to find the next unique workday not in the list.

OUTPUT

Note: The MAP function can be changed to the BYROW function, and it should produce the same result.