See the error in both 3.6.1.2 and 3.6.2.1 Trying to edit an array formula, either by F2 or by clicking on the fx box. Receive message: You cannot change only part of an array
To edit an array formula you need select the entire range. It works this way will all spreadsheets apps since decades. You can use Ctrl+/ combinaison key for highlight the array range.