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Hi and welcome to the Forum
You can use the LARGE function but with an array of numbers 1-10 (in curly brackets)- that will return the 10 highest number (most recent dates) in column F.
Those numbers can be used in MATCH to get the rows in column F which are then used in INDEX to get the values from cells in the 23rd column of the range F:AB (since the 1st column of that range is F and AB is the 23rd).
Finally those values are then caculated in the AVERAGE formula.
It's an array formula so in Excel 365 you just need to paste this in a cell:
=AVERAGE(INDEX(F:AB,MATCH(LARGE(F:F, {1,2,3,4,5,6,7,8,9,10}),F:F,0),23))
In earlier versions of Excel, you'll need to use Ctrl + Shift + Enter to input the formula.
If you also need to highlight the differential numbers associated with the 10 highest dates in column F say, you can create a new rule for cell AB2, based on value and use this formula (note there's only a single $ sign to lock the column to F but not the row):
=IF(RANK.EQ($F2,F:F,0)<=10,1,0)
and set a fill then edit the Applies to field to cover the contents of AB.
If there's existing conditional formatting there (say Top 20), you'd need to 'promote' the new rule so it appears above the existing rule (so that your new formatting appear on top ). Just change the 10 in bold above to give a different set (e.g. 3 for the differentials associated with the 3 highest dates)
Altermatively could use the LARGE function to create a series of rules, this being one to identify the cell in AB relating to the 2nd (highest) date:
=IF($F2=LARGE(F:F, 2),1,0)
Hope this works for you.