WordPress theme – defined in URL

I have googled and searched here for a decent amount of time and I’m now tossing in the towel and asking for help.

Is there are plugin that allows for a theme to be defined in the url (eg ?p=1&theme=classic)?

If not is there a plugin like Alex King uses ( https://www.alexking.org/software/wordpress/theme_browser.php )?

Thanks, Andy