does the keyboard accessibility feature on a macbook pro 16 change it to a touchscreen

No, it just puts a picture of the keyboard up on the display, and you can mouse-over a key and mouse-click on that key to effect a keyboard-press.

Touch screen requires specific Hardware changes, not currently supported except on the Touch Bar in Macs that have a Touch Bar.

You can connect a touch-screen iPad, and use it, and also use Apple pencil with that iPad on certain models of iPad.

For more info see

Use the Accessibility Keyboard on Mac - Apple Support