There is a classic Financial Modeling problem in Excel. You are checking values in each month and you end up with a row of zero and one values. How can you find the last month where you have a one?
Dan explains the classic technique of a Helper Row to identify the last one and then INDEX and MATCH.
Bill uses the Last to First Search Mode in XLOOKUP.
But then the shortest method – MAXIFS as suggested by Diarmid Early.

Table of Contents
(0:00) Welcome and the problem
(2:54) Solving with a helper row
(6:00) Using XLOOKUP
(7:47) Using MAXIFS