getpivotdata function with slicers

I wouldn't try it with getpivotdata, I don't like that formula for some reason.

If you want to extract the value from the pivot table, you could use:
=INDEX(Sayfa2!$C$4:$C$16;MATCH(TEXT(MAX($B$2:$B$27);"mmm");Sayfa2!$A$4:$A$16;0))

It looks in the source data to find the max date and extracts the "mmm" from it, then looks for that mmm in the pivot sheet and extracts the corresponding value.

You could also work with a formula on the source data of the pivot to make an average of the values from latest month.