Sorry to hear about the problem you are having.
I have tested it on my test site and it’s working fine for me using the latest version of the Ivory Search plugin.
I can see in your shared screenshot that the 500 Internal Server Error is causing the problem which is server related issue.
You can resolve 500 Internal Server Error as described on the below pages and also contact your web host to resolve it.
https://www.wpbeginner.com/wp-tutorials/how-to-fix-the-internal-server-error-in-wordpress/
How to Fix the 500 Internal Server Error in WordPress
How to Fix the 500 Internal Server Error on Your WordPress Website
Best regards,
Ivory Search Support