to anyone else wondering: you can browse the available function with the button to the right. ( SUM, AVERAGE, MIN, MAX and CONCAT )
https://exceljet.net/excel-functions/excel-sumproduct-functi...
All I can say is, I am grateful I don’t have to deal with other people’s spreadsheets.
My jam is programming languages and SQL, not obscure formulas and weird constructs made from surprising ways of using them.