Array formula not working in my computer

california2007 

Sorry, but I disagree.  To use 365 as if nothing has changed is a dreadful choice.  True Mike Girvin puts out some great material with more tricks than a cart load of monkeys, but the game has changed.  All of the time-honoured tricks with AGGREGATE (to compress a list of indices) and ROW (to generate a sequence of numbers) are no longer needed.

= FILTER(Table, (SalesRep=SelectedRep)*(Date=selectedDate))

is neater or, padding it out

= LET(
    repCriterion,  (SalesRep=selectedRep)+(selectedRep=""),
    dateCriterion, (Date=selectedDate)+(selectedDate=""),
    FILTER(Table, repCriterion*dateCriterion)
  )

is more flexible in terms of catering for omitted criteria.  Similarly, Mike's other formula would now be

= TAKE(SORTBY(UnitsRep, Units,-1), Top)

or, failing that,

= INDEX(
    SORTBY(UnitsRep, Units,-1), 
    SEQUENCE(Top),
    {1,2}
  )

california2007 

Yes, AGGREGATE always works, it is natively works with arrays. However, with 365 you may use dynamic arrays or Power Query. If not to be complex, as in attached file