How to create a Stacked Column Chart with a growth indicator (% bracket between bars)?

Hello ENF27,
Short answer no, you can't do this with a plain stacked column chart. Data labels and reference lines are about as far as the native visual goes; there's nothing built in that lets you draw a bracket connecting two bars with a % sitting in the middle.
A few ways to get around it:
Fake it with shapes/text boxes layered over the chart. Cheap to set up but it's static, resize the visual or change the data and the bracket no longer lines up.
Build it properly in Deneb https://deneb-viz.github.io/ , it's Vega-Lite under the hood so you get full control over annotations, free.
Or just use Zebra BI https://zebrabi.com/  or Inforiver https://inforiver.com ,  both handle variance/comparison visuals like this out of the box, no custom coding needed.
For reference: Create and use column charts in Power BI