how do I add support for windowed mode [Or, small windowed mode, free form window, floating window, etc. ]?

Question

Details:

I have been searching for this for a while. I want my android app to also have this support. I got answers such as android:resizeableActivity="true" didn't do much. I can't find a clear documentation or tutorial or even samples for achieving this. I want the entire app to support floating windowed mode such as shown in the screenshot given below.

I want to be clear, I AM NOT LOOKING FOR POP-UP WINDOW SUPPORT SUCH AS ONES PROVIDED BY YOUTUBE OF BROWSERS.

Example of what I am looking for:

A sample of windowed mode I am looking for. (here, chrome is in windowed mode)

This image shows the button used to enter windowed mode. (i.e. Small window button)