Thanks for your reply.
No the double quotes are being generated by the website here not from my code.
No display-posts is part of the core WordPress codex: https://wordpress.com/support/display-posts-shortcode/
This should be working but it is not.
I tried your suggestion and it is still displaying the raw shortcodes parameter instead of the expected output. That means that something has been overwritten in the core WordPress code. I don’t mess with any of the PHP or other code on my site so it is something happening that is messing the WordPress installation.
Please help.