Keyboard symbols

That curlicue key switches into the so-called handwriting or drawing mode.

For those unfamiliar, launch Messages.app, and switch your device to landscape orientation, and then press that button.

You’ll get a window where you can input free-form.

Or press the button there and get back to keyboard input.

Put differently, try it.

Hello,

This allows you to write a handwritten message. This is most useful with an Apple Pencil.

I wonder, do you have a stylus attached or are you in an app that supports handwriting?