Contact form in "Final screen"

Depending on the exact plugin you use it might be impossible. The final screen is called by ajax and some plugins won’t work this way.

Don’t know, I’m not familiar with all plugins in the world.
A workaround would be to give a link to the feedback form instead of embedding it. Or enter the static HTML code if such can be extracted or is provided.

I don’t use anything, never had the idea to include contact form on the final screen. You’ll have to find some solution yourself.

Thanks, good luck. A hint: you’ll need a plugin that allows using shortcode. Shortcodes are processed on the final screen. There is still no guarantee it will work out of the box because many plugins call some javascript on page load, and page load does not happen when submitting quiz by ajax.