Data Label Display Problem on Stacked Charts

"I don't know why but there is not "outside" options in position selection either. I could show data label at least as call-out at outside of bar."

I have the same issue and this is by no means a solution, but a workaround:

If you have always the same categories and time interval in your charts, one way to have the value displayed dynamically is to create a measure of it, put it in a card visual, remove the category, use a small font size for the label and place it as if it was part of your chart. Of course that its position will always remain the same, so use a font color (or background) that allows it to be visible either in front of the chart background or the column.

As I said, I know this is not a solution to your issue (as there is none currently), but if you want to mark this as solution, I'll be grateful.