Technical issue - expansion of the dialog box

Hi,

I have watched prompt creation video in which the presenter had an option of expanding the Copilot dialogue box into the full screen.

Upon pasting several line of text,

an arrow appeared in the top right corner of the dialog box (see photo attached)

This is for some unknown reason not available to me. Initially

I thought it's because I was using browser rather than the app, but I have since installed the app and I cannot find the way to replicate this. I'm let to believe that I have full unrestricted license.

What could be the cause of it? What am I missing?

Regards

Tom