The question is pretty straight forward: If I'm using a formula that will populate the column with a unknown range of data, no matter what formula it is (filter, query, arrayformula, unique), how would I make a row, or at least a cell, to be automatically placed right bellow the last cell of the populated data?
Here's what I would use:
=LET(data,<your_formula>,
{data;SUM(data)})
For example:
=LET(data,FILTER(A1:A5,B1:B5),
{data;SUM(data)})